Nonaqueous electrolyte solution and electricity storage device using same

ABSTRACT

The present invention provides a nonaqueous electrolytic solution capable of improving electrochemical characteristics in a broad temperature range and an energy storage device using the same. [1] A nonaqueous electrolytic solution having an electrolyte salt dissolved in a nonaqueous solvent, the nonaqueous electrolytic solution containing, as an additive, an SO 4  group-containing compound having a specified structure and [2] an energy storage device including a positive electrode, a negative electrode, and a nonaqueous electrolytic solution having an electrolyte salt dissolved in a nonaqueous solvent, wherein the nonaqueous electrolytic solution contains, as an additive, 0.001% by mass or more and less than 5% by mass of an SO 4  group-containing compound having a specified structure in the nonaqueous electrolytic solution, are disclosed.

TECHNICAL FIELD

The present invention relates to a nonaqueous electrolytic solutioncapable of improving electrochemical characteristics in a broadtemperature range and an energy storage device using the same.

In addition, the present invention relates to a nonaqueous electrolyticsolution capable of improving electrochemical characteristics at hightemperatures and high voltages and an energy storage device using thesame.

BACKGROUND ART

An energy storage device, especially a lithium secondary battery, hasbeen widely used recently for a power source of a small-sized electronicdevice, such as a mobile telephone, a notebook personal computer, etc.,and a power source for an electric vehicle or electric power storage.Since there is a possibility that such an electronic device or a vehicleis used in a broad temperature range, such as a high temperature inmidsummer, a low temperature in an extremely cold region, etc., it isdemanded to improve electrochemical characteristics with a good balancein a broad temperature range.

In particular, in order to prevent the global warming, it is an urgentneed to reduce the CO₂ emission. Among eco-friendly vehicles mountedwith an energy storage apparatus composed of an energy storage device,such as lithium secondary batteries, capacitors, etc., earlydissemination of a hybrid electric vehicle (HEV), a plug-in hybridelectric vehicle (PHEV), or a battery electric vehicle (BEV) isdemanded.

Since a vehicle is long in moving distance, there is a possibility thatthe vehicle is used in regions in a broad temperature range of from avery hot region of the torrid zone to an extremely cold region. Inconsequence, in particular, these onboard energy storage devices arerequired such that even when used in a broad temperature range of fromhigh temperatures to low temperatures, the electrochemicalcharacteristics are not worsened.

In the present specification, the term, lithium secondary battery, isused as a concept also including a so-called lithium ion secondarybattery.

A lithium secondary battery is mainly constituted of a positiveelectrode and a negative electrode, each containing a material capableof absorbing and releasing lithium, and a nonaqueous electrolyticsolution containing a lithium salt and a nonaqueous solvent, and acarbonate, such as ethylene carbonate (EC), propylene carbonate (PC),etc., is used as the nonaqueous solvent.

In addition, metallic lithium, a metal compound capable of absorbing andreleasing lithium (e.g., a metal elemental substance, a metal oxide, analloy with lithium, etc.), and a carbon material are known as thenegative electrode. In particular, a lithium secondary battery using acarbon material capable of absorbing and releasing lithium, such ascoke, artificial graphite, natural graphite, etc., is widely put intopractical use.

For example, in a lithium secondary battery using, as the negativeelectrode material, a highly crystallized carbon material, such asnatural graphite, artificial graphite, etc., it is known that adecomposition product or gas generated by reductive decomposition of asolvent in a nonaqueous electrolytic solution on the negative electrodesurface on charging hinders a desired electrochemical reaction of thebattery, so that worsening of cycle properties is possibly caused. Whendecomposition products of the nonaqueous solvent are accumulated,absorption and release of lithium on the negative electrode may not beperformed smoothly, and the electrochemical characteristics when used ina broad temperature range are liable to be worsened.

Furthermore, it is known that a lithium secondary battery using alithium metal or an alloy thereof, or a metal elemental substance, suchas tin, silicon, etc., or an oxide thereof as the negative electrodematerial may have a high initial battery capacity, but the batteryperformance thereof, such as battery capacity and cycle properties, maybe largely worsened because the micronized powdering may be promotedduring cycles, thereby bringing about accelerated reductivedecomposition of the nonaqueous solvent, as compared with the negativeelectrode formed of a carbon material. When such a negative material ismicronized, or decomposition products of the nonaqueous solvent areaccumulated, absorption and release of lithium on the negative electrodemay not be performed smoothly, and the electrochemical characteristicswhen used in a broad temperature range are liable to be worsened.

Meanwhile, it is known that in a lithium secondary battery using, as apositive electrode material, for example, LiCoO₂, LiMn₂O₄, LiNiO₂,LiFePO₄, etc., on an interface between the positive electrode materialand the nonaqueous electrolytic solution in such a state that thenonaqueous solvent in the nonaqueous electrolytic solution is charged, adecomposition product or gas generated by a partial oxidativedecomposition which is caused locally hinders a desired electrochemicalreaction of the battery, and therefore, the electrochemicalcharacteristics when used in a broad temperature range are liable to beworsened, too.

In the light of the above, the battery performance was worsened due tothe matter that the movement of a lithium ion is hindered or the batteryis expanded by a decomposition product or gas when the nonaqueouselectrolytic solution is decomposed on the positive electrode ornegative electrode. Irrespective of such a situation, themultifunctionality of electronic devices on which lithium secondarybatteries are mounted is more and more advanced, and power consumptiontends to increase. For that reason, the capacity of lithium secondarybattery is thus being much increased, and the space volume for thenonaqueous electrolytic solution in the battery is decreased byincreasing the density of the electrode, or reducing the useless spacevolume in the battery, or the like. In consequence, it is a situationthat the electrochemical characteristics when used in a broadtemperature range are liable to be worsened due to even a bit ofdecomposition of the nonaqueous electrolytic solution.

PTL 1 proposes a nonaqueous electrolyte secondary battery containing asulfuric acid ester compound, such as dimethyl sulfate, etc., for thepurpose of increasing cycle properties and suggests that in view of thefact that such a compound reacts on the negative electrode surface toform a surface film, the cycle properties are improved.

PTL 2 proposes an electrochemical battery containing a sulfuric acidester compound, such as methyl sulfate, etc., for the purpose ofimproving a first cycle irreversible capacity and keeping alow-temperature cycle capacity and suggests that in view of the factthat such a compound reacts on the negative electrode surface to form asurface film, the first cycle irreversible capacity is improved.

PTL 3 proposes a secondary battery containing, as an anionic activeagent, an alkyl sulfate, such as lithium dodecylsulfate, etc., for thepurpose of improving high-rate discharging properties and suggests thatby improving wettability of the negative electrode, the high-ratedischarging properties are improved.

PTL 4 proposes a secondary battery containing a cyclic disulfonic acidester and a surfactant for the purpose of improving a long-term cyclelife and suggests that wettability of an electrolytic solution to anegative electrode is improved so that the cyclic disulfonic acid esterpenetrates into details, whereby SEI is uniformly formed and the cycleproperties are improved.

In general, as an electrolyte salt which is used for energy storagedevices, such as lithium secondary batteries, etc., an electrolytehaving sufficient solubility in an organic solvent, for example, LiPF₆,LiBF₄, LiClO₄, LiN(SO₂CF₃)₂, LiN(SO₂C₂F₅)₂, LiCF₃SO₃, etc., is selected,and of those, especially, LiPF₆ is widely used (PTLs 5 and 6, etc.).

PTL 7 discloses a nonaqueous electrolytic solution containing LiPF₆ as amain lithium salt, to which a small amount of a perfluoroalkane sulfonicacid salt, such as lithium perfluorobutanesulfonate (LiPFBS), etc. andindicates that not only the charging and discharging cycle propertiesmay be improved, but also the time for injecting the electrolyticsolution into a battery may be shortened.

CITATION LIST Patent Literature

PTL 1: JP-A 9-245833

PTL 2: JP-A 2001-176548

PTL 3: JP-A 8-306386

PTL 4: JP-A 2008-71559

PTL 5: JP-A 5-290844

PTL 6: JP-A 7-235321

PTL 7: JP-A 2008-198409

SUMMARY OF INVENTION Technical Problem

A problem of the present invention is to provide a nonaqueouselectrolytic solution capable of improving electrochemicalcharacteristics in a broad temperature range, and an energy storagedevice using the same.

In addition, a problem of the present invention is to provide anonaqueous electrolytic solution capable of improving electrochemicalcharacteristics at high temperatures and high voltages, and an energystorage device using the same.

Solution to Problem

The present inventors made extensive and intensive investigationsregarding the performances of the nonaqueous electrolytic solutions ofthe aforementioned conventional techniques. As a result, in thenonaqueous electrolyte secondary batteries of PTLs 1 to 7, it was theactual situation that the effects may not be substantially exhibitedwith respect to the problem that the electrochemical characteristics ina broad temperature range, such as low-temperature dischargingproperties after high-temperature storage, etc., are improved.

Then, in order to solve the foregoing problem, the present inventorsmade extensive and intensive investigations. As a result, it has beenfound that in a nonaqueous electrolytic solution having an electrolytesalt dissolved in a nonaqueous solvent, by incorporating a specified SO₄group-containing compound, electrochemical characteristics of an energystorage device, especially electrochemical characteristics of a lithiumbattery in a broad temperature range may be improved, leading toaccomplishment of the present invention. Such an effect is not suggestedat all in PTLs 1 to 7.

Though LiPF₆ is excellent in solubility in an organic solvent, itinvolves problems in heat resistance, hydrolysis properties, and thelike, and especially, it was the actual situation that LiPF₆ may notsubstantially bring about an effect with respect to a problem ofimproving a gas generation suppressing effect at high temperatures andhigh voltages. Even if a perfluoroalkanesulfonate represented byLiCF₃SO₃ is added to a nonaqueous electrolytic solution using LiPF₆ as amain lithium salt, the foregoing problem could not be solved.

Then, in order to solve the foregoing problem, the present inventorsmade extensive and intensive investigations. As a result, it has beenfound that in a nonaqueous electrolytic solution having an electrolytesalt dissolved in a nonaqueous solvent, by incorporating a specified SO₄group-containing compound in a specified addition amount,electrochemical characteristics of an energy storage device, especiallyelectrochemical characteristics of a lithium battery at hightemperatures and high voltages may be improved.

Specifically, the present invention provides the following (1) and (2).

(1) A nonaqueous electrolytic solution having an electrolyte saltdissolved in a nonaqueous solvent, the nonaqueous electrolytic solutioncomprising, as an additive, at least one selected from SO₄group-containing compounds represented by any one of the followinggeneral formulae (I) to (IV);

wherein L¹ represents an alkyl group having 1 to 12 carbon atoms, analkoxyalkyl group having 2 to 12 carbon atoms, an aryl group having 6 to12 carbon atoms, an alkenyl group having 2 to 7 carbon atoms, an alkynylgroup having 3 to 8 carbon atoms, a linear or cyclic ester group having3 to 18 carbon atoms, a sulfur atom-containing organic group having 1 to6 carbon atoms, a silicon atom-containing organic group having 4 to 10carbon atoms, a cyano group-containing organic group having 2 to 7carbon atoms, a phosphorus atom-containing organic group having 2 to 12carbon atoms, a —P(═O)F₂ group, an alkylcarbonyl group having 2 to 7carbon atoms, or an arylcarbonyl group having 7 to 13 carbon atoms,

provided that each of the alkyl group, the alkoxyalkyl group, thealkenyl group, the alkynyl group, and the alkylcarbonyl group isstraight-chain or branched, and in each of the alkyl group, thealkoxyalkyl group, the aryl group, the ester group, the sulfuratom-containing organic group, the phosphorus atom-containing organicgroup, the alkylcarbonyl group, and the arylcarbonyl group, at least onehydrogen atom may be substituted with a halogen atom;

wherein L² represents a p-valent hydrocarbon connecting group which maycontain an ether bond, a thioether bond, or an —S(═O)₂ bond, and p is aninteger of 2 to 4, provided that at least one hydrogen atom which L² hasmay be substituted with a halogen atom;

wherein each of R³¹ to R³³ independently represents an alkyl grouphaving 1 to 12 carbon atoms, an alkenyl group having 2 to 3 carbonatoms, or an aryl group having 6 to 8 carbon atoms, and q is an integerof 1 to 4,

when q is 1, then R³¹ may be —OSO₃—R³⁷, and R³⁷ is synonymous with R³¹,

when q is 1, then L³ represents an alkyl group having 1 to 12 carbonatoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl grouphaving 3 to 6 carbon atoms, an alkoxyalkyl group having 2 to 12 carbonatoms, a —CR³⁴R³⁵C(═O)OR³⁶ group, or an aryl group having 6 to 12 carbonatoms, and when q is 2 to 4, then L³ represents a q-valent hydrocarbonconnecting group which may contain an ether bond, a thioether bond, oran —S(═O)₂— bond,

each of R³⁴ and R³⁵ independently represents a hydrogen atom, a halogenatom, or an alkyl group having 1 to 4 carbon atoms, and R³⁶ representsan alkyl group having 1 to 8 carbon atoms, an alkenyl group having 2 to6 carbon atoms, or an alkynyl group having 3 to 6 carbon atoms, and

in each of the alkyl group and the aryl group represented by L³, and thealkyl group represented by each of R³⁴ to R³⁶, at least one hydrogenatom may be substituted with a halogen atom; and

wherein L⁴ represents an alkyl group having 1 to 12 carbon atoms, analkenyl group having 2 to 6 carbon atoms, an alkynyl group having 3 to 6carbon atoms, an alkoxyalkyl group having 2 to 12 carbon atoms, a—CR⁴¹R⁴²C(═O)OR⁴³ group, or an aryl group having 6 to 12 carbon atoms, Xrepresents an SiR⁴⁴R⁴⁵ group, a quaternary onium, an alkali metalbelonging to the third or fourth period of the Periodic Table, or analkaline earth metal belonging to the third or fourth period of thePeriodic Table, and r is an integer of 1 or 2,

provided that when X is a quaternary onium or an alkali metal belongingto the third or fourth period of the Periodic Table, then r is 1, andwhen X is an SiR⁴⁴R⁴⁵ group or an alkaline earth metal belonging to thethird or fourth period of the Periodic Table, then r is 2,

each of R⁴¹ and R⁴² independently represents a hydrogen atom, a halogenatom, or an alkyl group having 1 to 4 carbon atoms, R⁴³ represents analkyl group having 1 to 8 carbon atoms, an alkenyl group having 2 to 6carbon atoms, or an alkynyl group having 3 to 6 carbon atoms, and eachof R⁴⁴ and R⁴⁵ independently represents an alkyl group having 1 to 12carbon atoms, an alkenyl group having 2 to 3 carbon atoms, or an arylgroup having 6 to 8 carbon atoms, and

in each of the alkyl group and the aryl group, at least one hydrogenatom may be substituted with a halogen atom.

The Periodic Table as referred to in the present specification means agenerally used Long Periodic Table.

(2) An energy storage device comprising a positive electrode, a negativeelectrode, and a nonaqueous electrolytic solution having an electrolytesalt dissolved in a nonaqueous solvent, wherein the nonaqueouselectrolytic solution contains, as an additive, 0.001% by mass or moreand less than 5% by mass of at least one selected from the SO₄group-containing compounds represented by any one of the foregoinggeneral formulae (I) to (IV) in the nonaqueous electrolytic solution.

Advantageous Effects of Invention

According to the present invention, it is possible to provide anonaqueous electrolytic solution capable of improving electrochemicalcharacteristics of an energy storage device in a broad temperaturerange, especially low-temperature discharging properties afterhigh-temperature storage and an energy storage device using the same,such as a lithium battery, etc.

In addition, according to the present invention, it is possible toprovide a nonaqueous electrolytic solution capable of improvingelectrochemical characteristics of an energy storage device at hightemperatures and high voltages, especially a gas generation suppressingeffect at high temperatures and high voltages, and an energy storagedevice using the same, such as a lithium battery, etc.

DESCRIPTION OF EMBODIMENTS

The present invention relates to a nonaqueous electrolytic solution andan energy storage device using the same.

[Nonaqueous Electrolytic Solution]

The nonaqueous electrolytic solution of the present invention is anonaqueous electrolytic solution having an electrolyte salt dissolved ina nonaqueous solvent, the nonaqueous electrolytic solution comprising,as an additive, at least one selected from SO₄ group-containingcompounds represented by any one of the foregoing general formulae (I)to (IV).

Although the reason why the nonaqueous electrolytic solution of thepresent invention is capable of significantly improving electrochemicalcharacteristics of an energy storage device in a broad temperature rangehas not always been elucidated yet, the following may be considered.

The SO₄ group-containing compound which is used in the present inventionis a compound in which one hydrogen atom of sulfuric acid is substitutedwith an alkyl group, an alkoxyalkyl group, an aryl group, an alkenylgroup, an alkynyl group, a linear or cyclic ester group, analkylcarbonyl group, an arylcarbonyl group, a sulfur atom-containingorganic group, a silicon atom-containing organic group, a cyanogroup-containing organic group, or a phosphorus atom-containing organicgroup, each having a specified carbon number, or a —P(═O)F₂ group, andthe other hydrogen atom of sulfuric acid is substituted with an alkalimetal, such as lithium, etc., an alkaline earth metal, such asmagnesium, etc., a quaternary onium, or a silyl group. According to thischaracteristic feature on chemical structure, a part of the SO₄group-containing compound of the present invention is decomposed on anegative electrode, thereby forming a surface film and is alsodecomposed on a positive electrode, thereby forming a surface film withlow electric resistance. It may be considered that in view of the factthat the surface film is formed on both the positive electrode and thenegative electrode in this way, the effect for improving electrochemicalcharacteristics in a broad temperature range, the effect being not seenin a dialkyl sulfate in which the both hydrogen atoms of sulfuric acidare substituted with an alkyl group, or a monoalkyl sulfate in whichonly one hydrogen of sulfuric acid is substituted with an alkyl group,is more increased. In particular, since the monoalkyl sulfate is astrong acid, the metal elution of the positive electrode is acceleratedat the time of high-temperature storage, whereby the capacity is greatlydecreased. However, it has become clear that since the SO₄group-containing compound of the present invention is not a strong acid,the electrochemical characteristics of an energy storage device may beremarkably improved in a broad temperature range.

Other SO₄ group-containing compound which is used in the presentinvention is a compound in which plural SO₄ groups in which one hydrogenatom of sulfuric acid is substituted with lithium or a silyl group areconnected with each other via a hydrocarbon group. According to thischaracteristic feature on chemical structure, a part of the SO₄group-containing compound of the present invention is decomposed on anegative electrode, thereby forming a surface film and is alsodecomposed on a positive electrode, thereby forming a surface film withlow electric resistance. As a result, similar to the foregoing, it maybe considered that the effect for improving electrochemicalcharacteristics in a broad temperature range has been much moreincreased.

Though the reason why the nonaqueous electrolytic solution of thepresent invention using, as the SO₄ group-containing compoundrepresented by the general formula (I), a halogen-substituted SO₄group-containing compound represented by the general formula (I-3) asdescribed later is capable of significantly improving electrochemicalcharacteristics of an energy storage device at high temperatures andhigh voltages has not always been elucidated yet, the following may beconsidered.

LiPF₆ which is generally used as a main electrolyte salt is liable to bedecomposed, and especially, the decomposition proceeds at hightemperatures and high voltages, whereby a hydrogen fluorideconcentration in the electrolytic solution increases, and the nonaqueoussolvent is decomposed, resulting in worsening of the electrochemicalcharacteristics. In the case where the SO₄ group-containing compoundwhich is used in the present invention is a fluorine-containingmono-substituted lithium sulfate in which one hydrogen atom of sulfuricacid is substituted with an alkyl group in which at least one hydrogenatom is substituted with a halogen atom, an alkoxyalkyl group in whichat least one hydrogen atom is substituted with a halogen atom, or anaryl group in which at least one hydrogen atom is substituted with ahalogen atom, and the other hydrogen atom is substituted with lithium,the fluorine-containing mono-substituted lithium sulfate is high insolubility in the electrolytic solution and also high in stability athigh temperatures. For this reason, it has been understood that bysubstituting the whole or a part of LiPF₆ as the main electrolyte saltwith a halogen atom, the effect for improving electrochemicalcharacteristics in a much broader temperature range is increased becausethe halogen atom concentration in the electrolytic solution does notincrease, or the nonaqueous solvent is not decomposed.

The SO₄ group-containing compound which is contained in the nonaqueouselectrolytic solution of the present invention is represented by any oneof the foregoing general formulae (I) to (IV).

The SO₄ group-containing compound represented by any one of the generalformulae (I) to (IV) is hereunder successively explained.

[SO₄ Group-Containing Compounds Represented by the General Formula (I)]

In the general formula (I), L¹ represents an alkyl group having 1 to 12carbon atoms, an alkoxyalkyl group having 2 to 12 carbon atoms, an arylgroup having 6 to 12 carbon atoms, an alkenyl group having 2 to 7 carbonatoms, an alkynyl group having 3 to 8 carbon atoms, a linear or cyclicester group having 3 to 18 carbon atoms, a sulfur atom-containingorganic group having 1 to 6 carbon atoms, a silicon atom-containingorganic group having 4 to 10 carbon atoms, a cyano group-containingorganic group having 2 to 7 carbon atoms, a phosphorus atom-containingorganic group having 2 to 12 carbon atoms, a —P(═O)F₂ group, analkylcarbonyl group having 2 to 7 carbon atoms, or an arylcarbonyl grouphaving 7 to 13 carbon atoms.

However, each of the alkyl group, the alkoxyalkyl group, the alkenylgroup, the alkynyl group, and the alkylcarbonyl group is straight-chainor branched, and in each of the alkyl group, the alkoxyalkyl group, thearyl group, the ester group, the sulfur atom-containing organic group,the phosphorus atom-containing organic group, the alkylcarbonyl group,and the arylcarbonyl group, at least one hydrogen atom may besubstituted with a halogen atom.

Suitable examples of the SO₄ group-containing compound represented bythe general formula (I) include compounds represented by the followinggeneral formula (I-1):

In the formula (I-1), L¹¹ represents an alkyl group having 1 to 12carbon atoms, an alkoxyalkyl group having 2 to 12 carbon atoms, or anaryl group having 6 to 12 carbon atoms, provided that, in each of thealkyl group, the alkoxyalkyl group, and the aryl group, at least onehydrogen atom may be substituted with a halogen atom.

In the foregoing general formula (I-1), L¹¹ is preferably astraight-chain or branched alkyl group having 1 to 8 carbon atoms, inwhich at least one hydrogen atom may be substituted with a halogen atom,an alkoxyalkyl group having 2 to 8 carbon atoms, in which at least onehydrogen atom may be substituted with a halogen atom, or an aryl grouphaving 6 to 10 carbon atoms, in which at least one hydrogen atom may besubstituted with a halogen atom; more preferably a straight-chain orbranched alkyl group having 1 to 6 carbon atoms, in which at least onehydrogen atom may be substituted with a halogen atom, an alkoxyalkylgroup having 2 to 6 carbon atoms, or an aryl group having 6 to 9 carbonatoms, in which at least one hydrogen atom may be substituted with ahalogen atom; and still more preferably a straight-chain or branchedalkyl group having 1 to 5 carbon atoms, and preferably 1 to 4 carbonatoms, in which at least one hydrogen atom may be substituted with ahalogen atom, an alkoxyalkyl group having 2 to 4 carbon atoms, in whichat least one hydrogen atom may be substituted with a halogen atom, or anaryl group having 6 to 8 carbon atoms, in which at least one hydrogenatom may be substituted with a halogen atom.

As specific examples of L¹¹, there are suitably exemplified astraight-chain alkyl group, such as a methyl group, an ethyl group, ann-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group,an n-heptyl group, an n-octyl group, an n-decyl group, an n-dodecylgroup, etc.; a branched alkyl group, such as an isopropyl group, asec-butyl group, a tert-butyl group, a tert-amyl group, a 2-ethylhexylgroup, etc.; a fluoroalkyl group, such as a fluoromethyl group, adifluoromethyl group, a trifluoromethyl group, a 2-fluoroethyl group, a2,2-difluoroethyl group, a 2,2,2-trifluoroethyl group, a 3-fluoropropylgroup, a 3,3-difluoropropyl group, a 3,3,3-trifluoropropyl group, a2,2,3,3-tetrafluoropropyl group, a 2,2,3,3,3-pentafluoropropyl group, a1,1,1,3,3,3-hexafluoro-2-propyl group, etc.; an alkoxyalkyl group, suchas a methoxymethyl group, an ethoxymethyl group, a methoxyethyl group,an ethoxyethyl group, an n-propoxyethyl group, an n-butoxyethyl group,an n-hexyloxyethyl group, a methoxypropyl group, an ethoxypropyl group,etc.; a fluoroalkoxyalkyl group, such as a fluoromethoxymethyl group, adifluoromethoxymethyl group, a trifluoromethoxymethyl group, a2-fluoroethoxymethyl group, a 2,2-difluoroethoxymethyl group, a2,2,2-trifluoroethoxymethyl group, a fluoromethoxyethyl group, adifluoromethoxyethyl group, a trifluoromethoxyethyl group, a2-fluoroethoxyethyl group, a 2,2-difluoroethoxyethyl group, a2,2,2-trifluoroethoxymethyl group, etc.; and an aryl group, such as aphenyl group, a 2-methylphenyl group, a 3-methylphenyl group, a4-methylphenyl group, a 4-tert-butylphenyl group, a 2-fluorophenylgroup, a 4-fluorophenyl group, a 4-trifluoromethylphenyl group, a2,4-difluorophenyl group, a perfluorophenyl group, etc.

Of those, a methyl group, an ethyl group, an n-propyl group, an n-butylgroup, an n-pentyl group, an n-hexyl group, an n-heptyl group, ann-octyl group, an isopropyl group, a sec-butyl group, a trifluoromethylgroup, a 2,2,2-trifluoroethyl group, a 2,2,3,3-tetrafluoropropyl group,a methoxyethyl group, an ethoxyethyl group, an n-propoxyethyl group, ann-butoxyethyl group, an n-hexyloxyethyl group, a methoxypropyl group, anethoxypropyl group, a fluoromethoxyethyl group, a2,2,2-trifluoroethoxymethyl group, a phenyl group, a 4-methylphenylgroup, a 4-fluorophenyl group, and a perfluorophenyl group arepreferred; a methyl group, an ethyl group, an n-propyl group, an n-butylgroup, an n-pentyl group, an n-hexyl group, an isopropyl group, asec-butyl group, a trifluoromethyl group, a 2,2,2-trifluoroethyl group,a methoxyethyl group, an ethoxyethyl group, an n-propoxyethyl group, ann-butoxyethyl group, a methoxypropyl group, an ethoxypropyl group, aphenyl group, a 4-methylphenyl group, a 4-fluorophenyl group, and aperfluorophenyl group are more preferred; and a methyl group, an ethylgroup, an n-propyl group, an n-butyl group, an isopropyl group, a2,2,2-trifluoroethyl group, a 2,2,3,3-tetrafluoropropyl group, amethoxyethyl group, a methoxypropyl group, a phenyl group, and a4-fluorophenyl group are still more preferred.

Specifically, examples of the SO₄ group-containing compound representedby the foregoing general formula (I-1) include the following compounds.

There are suitably exemplified lithium methyl sulfate, lithium ethylsulfate, lithium propyl sulfate, lithium butyl sulfate, lithium pentylsulfate, lithium hexyl sulfate, lithium heptyl sulfate, lithium octylsulfate, lithium decyl sulfate, lithium dodecyl sulfate, lithiumisopropyl sulfate, lithium sec-butyl sulfate, lithium tert-butylsulfate, lithium tert-amyl sulfate, lithium 2-ethylhexyl sulfate,lithium fluoromethyl sulfate, lithium difluoromethyl sulfate, lithiumtrifluoromethyl sulfate, lithium 2-fluoroethyl sulfate, lithium2,2-difluoroethyl sulfate, lithium 2,2,2-trifluoroethyl sulfate, lithium3-fluoropropyl sulfate, lithium 3,3-difluoropropyl sulfate, lithium3,3,3-trifluoropropyl sulfate, lithium 2,2,3,3-tetrafluoropropylsulfate, lithium 2,2,3,3,3-pentafluoropropyl sulfate, lithium1,1,3,3,3-hexafluoro-2-propyl sulfate, lithium methoxymethyl sulfate,lithium ethoxymethyl sulfate, lithium methoxyethyl sulfate, lithiumethoxyethyl sulfate, lithium n-propoxyethyl sulfate, lithiumn-butoxyethyl sulfate, lithium n-hexyloxyethyl sulfate, lithiummethoxypropyl sulfate, lithium ethoxypropyl sulfate, lithiumfluoromethoxymethyl sulfate, lithium difluoromethoxymethyl sulfate,lithium trifluoromethoxymethyl sulfate, lithium 2-fluoroethoxymethylsulfate, lithium 2,2-difluoroethoxymethyl sulfate, lithium2,2,2-trifluoroethoxymethyl sulfate, lithium fluoromethoxyethyl sulfate,lithium difluoromethoxyethyl sulfate, lithium trifluoromethoxyethylsulfate, lithium 2-fluoroethoxydethyl sulfate, lithium2,2-difluoroethoxyethyl sulfate, lithium 2,2,2-trifluoroethoxyethylsulfate, lithium phenyl sulfate, lithium 2-methylphenyl sulfate, lithium3-methylphenyl sulfate, lithium 4-methylphenyl sulfate, lithium4-tert-butylphenyl sulfate, lithium 2-fluorophenyl sulfate, lithium4-fluorophenyl sulfate, lithium 4-trifluoromethylphenyl sulfate, lithium2,4-difluorophenyl sulfate, and lithium perfluorophenyl sulfate.

Of the SO₄ group-containing compounds represented by the foregoinggeneral formula (I-1), one or more selected from lithium methyl sulfate,lithium ethyl sulfate, lithium propyl sulfate, lithium butyl sulfate,lithium pentyl sulfate, lithium hexyl sulfate, lithium heptyl sulfate,lithium octyl sulfate, lithium isopropyl sulfate, lithium sec-butylsulfate, lithium trifluoromethyl sulfate, lithium 2,2,2-trifluoroethylsulfate, lithium 2,2,3,3-tetrafluoropropyl sulfate, lithium1,1,3,3,3-hexafluoro-2-propyl sulfate, lithium methoxyethyl sulfate,lithium ethoxyethyl sulfate, lithium methoxypropyl sulfate, lithiumphenyl sulfate, lithium 4-methylphenyl sulfate, lithium 4-fluorophenylsulfate, and lithium perfluorophenyl sulfate are more preferred.

In the nonaqueous electrolytic solution of the present invention, acontent of the SO₄ group-containing compound represented by theforegoing general formula (I-1), which is contained in the nonaqueouselectrolytic solution, is preferably 0.001% by mass or more and lessthan 5% by mass in terms of an additive in the nonaqueous electrolyticsolution. So long as the content is less than 5% by mass, there is lessconcern that a surface film is excessively formed on the electrode,thereby worsening the low-temperature properties, and so long as thecontent is 0.001% by mass or more, the formation of a surface film issatisfactory, and the effect for improving high-temperature storageproperties is increased. Thus, the foregoing range is preferred. Thecontent is more preferably 0.05% by mass or more, and still morepreferably 0.1% by mass or more in the nonaqueous electrolytic solution.Its upper limit is more preferably 3% by mass or less, and still morepreferably 1% by mass or less.

Other suitable examples of the SO₄ group-containing compound representedby the general formula (I) include compounds represented by thefollowing general formula (I-2):

In the formula (I-2), L¹² represents a straight-chain or branchedalkenyl group having 2 to 7 carbon atoms, a straight-chain or branchedalkynyl group having 3 to 8 carbon atoms, a linear or cyclic ester grouphaving 3 to 18 carbon atoms, a linear or cyclic carbonate group having 3to 18 carbon atoms, a sulfur atom-containing organic group having 1 to 6carbon atoms, a silicon atom-containing organic group having 4 to 10carbon atoms, a cyano group-containing organic group having 2 to 7carbon atoms, a phosphorus atom-containing organic group having 2 to 12carbon atoms, a —P(═O)F₂ group, an alkylcarbonyl group having 2 to 7carbon atoms, or an arylcarbonyl group having 7 to 13 carbon atoms,provided that each of the alkenyl group, the alkynyl group, and thealkylcarbonyl group is straight-chain or branched, and in each of theester group, the sulfur atom-containing organic group, the phosphorusatom-containing organic group, the alkylcarbonyl group, and thearylcarbonyl group, at least one hydrogen atom may be substituted with ahalogen atom.

As specific examples of L¹², there are suitably exemplified thefollowing groups.

(i) The case where L¹² is a straight-chain or branched alkenyl grouphaving 2 to 7 carbon atoms:

As such an alkenyl group, a straight-chain or branched alkenyl grouphaving 2 to 6 carbon atoms is preferred, and a straight-chain orbranched alkenyl group having 2 to 5 carbon atoms is more preferred.Above all, a straight-chain alkenyl group, such as a vinyl group, a2-propenyl group, a 2-butenyl group, a 3-butenyl group, a 4-pentenylgroup, etc., and a branched alkenyl group, such as a 2-methyl-2-propenylgroup, a 2-methyl-2-butenyl group, a 3-methyl-2-butenyl group, etc., arepreferred, and a vinyl group and a 2-propenyl group are more preferred.

(ii) The case where L¹² is a straight-chain or branched alkynyl grouphaving 3 to 8 carbon atoms:

As such an alkynyl group, a straight-chain or branched alkynyl grouphaving 3 to 6 carbon atoms is preferred, and a straight-chain orbranched alkynyl group having 3 to 5 carbon atoms is more preferred.Above all, a straight-chain alkynyl group, such as a 2-propynyl group, a2-butynyl group, a 3-butynyl group, a 4-pentynyl group, a 5-hexynylgroup, etc., and a branched alkynyl group, such as a 1-methyl-2-propynylgroup, a 1-methyl-2-butynyl group, a 1,1-dimethyl-2-propynyl group,etc., are preferred, and a 2-propynyl group and a 1-methyl-2-propynylgroup are more preferred.

(iii) The case where L¹² is a linear or cyclic ester group having 3 to18 carbon atoms:

As such an ester group, substituents having a linear or cyclic estergroup having 3 to 15 carbon atoms are preferred, and substituents havinga linear or cyclic ester group having 3 to 10 carbon atoms, asrepresented by the following [Chem. 8] or [Chem. 9] are more preferred.

* in the formulae of the substituents shown in [Chem. 8] or [Chem. 9]represents a binding site in the foregoing formula (I-2), hereinafterthe same.

(iv) The case where L¹² is a linear or cyclic carbonate group having 3to 18 carbon atoms:

As such a carbonate group, substituents having a linear or cycliccarbonate group having preferably 3 to 10 carbon atoms, and morepreferably 3 to 8 carbon atoms are preferred. As especially preferredgroups, there are exemplified the following groups.

(v) The case where L¹² is a sulfur atom-containing organic group having1 to 6 carbon atoms:

As such an organic group, substituents having a sulfur atom-containingorganic group having preferably 1 to 5 carbon atoms, more preferably 1to 4 carbon atoms, and still more preferably 3 to 4 carbon atoms arepreferred. As especially preferred groups, there are exemplified thefollowing groups.

(vi) The case where L¹² is a silicon atom-containing organic grouphaving 4 to 10 carbon atoms:

As such an organic group, substituents having a silicon atom-containingorganic group having preferably 4 to 9 carbon atoms, and more preferably4 to 7 carbon atoms are preferred. As especially preferred groups, thereare exemplified the following groups.

(vii) The case where L¹² is a cyano group-containing organic grouphaving 2 to 7 carbon atoms:

As such an organic group, substituents having a cyano group-containingorganic group having preferably 2 to 6 carbon atoms, and more preferably2 to 5 carbon atoms are preferred. As especially preferred groups, thereare exemplified the following groups.

(viii) The case where L¹² is a phosphorus atom-containing organic grouphaving 2 to 12 carbon atoms or a —P(═O)F₂ group:

As such an organic group, substituents having a phosphorusatom-containing organic group having preferably 2 to 10 carbon atoms,and more preferably 3 to 8 carbon atoms and a —P(═O)F₂ group arepreferred. As especially preferred groups, there are exemplified thefollowing groups.

(ix) The case where L¹² is an alkylcarbonyl group having 2 to 7 carbonatoms or an arylcarbonyl group having 7 to 13 carbon atoms:

As such an organic group, an alkylcarbonyl group having 2 to 5 carbonatoms and an arylcarbonyl group having 7 to 10 carbon atoms arepreferred, and an alkylcarbonyl group having 2 to 3 carbon atoms and anarylcarbonyl group having 7 to 8 carbon atoms are more preferred. Asespecially preferred groups, there are exemplified the following groups.

Specifically, suitable examples of the SO₄ group-containing compoundrepresented by the foregoing general formula (I-2) include the followingcompounds.

(A) Compounds in which L¹² is a straight-chain or branched alkenylgroup:

(B) Compounds in which L¹² is a straight-chain or branched alkynylgroup:

(C) Compounds in which L¹² is a linear or cyclic ester group:

(D) Compounds in which L¹² is a linear or cyclic carbonate group:

(E) Compounds in which L¹² is a sulfur atom-containing organic group:

(F) Compounds in which L¹² is a silicon atom-containing organic group:

(G) Compounds in which L¹² is a cyano group-containing organic group:

(H) Compounds in which L¹² is a phosphorus atom-containing organic groupor a —P(═O)F₂ group:

(J) Compounds in which L¹² is an alkylcarbonyl group or an arylcarbonylgroup:

Among the SO₄ group-containing compounds represented by the foregoinggeneral formula (I-2), one or more selected from Compounds AA1, AA2,AA6, AB1, AB6, AC1, AC5, AC6, AC10 to AC12, AC17, AC18, AC21, AC23,AC30, AC32, AC34, AC36, AC37, AD1, AD4 to AD8, AE3, AE4, AE8 to AE11,AF2, AG2, AG4 to AG6, AH1, AH2, AH7 to AH10, AH15, AJ1, AJ5, AJ6, AJ8,and AJ9 are preferred, and one or more selected from lithium vinylsulfate (Compound AA1), lithium allyl sulfate (Compound AA2), lithiumpropargyl sulfate (Compound AB1), lithium1-oxo-1-ethoxy-1-oxopropan-2-yl sulfate (Compound AC6), lithium1-oxo-1-(2-propynyloxy)propan-2-yl sulfate (Compound AC11), lithium2-(acryloyloxy)ethyl sulfate (Compound AC30), lithium2-(methacryloyloxy)ethyl sulfate (Compound AC32), lithium2-((methoxycarbonyl)oxy)ethyl sulfate (Compound AD1), lithium(2-oxo-1,3-dioxolan-4-yl)methyl sulfate (Compound AD8), lithium2-(methanesulfonyl)ethyl sulfate (Compound AE3), lithium methanesulfonylsulfate (Compound AE4), lithium trifluoromethanesulfonyl sulfate(Compound AE9), lithium 2-(trimethylsilyl)ethyl sulfate (Compound AF2),lithium 2-cyanoethyl sulfate (Compound AG2), lithium 1,3-dicyanopropynyl2-sulfate (Compound AG6), lithium (diethoxyphosphoryl)methyl sulfate(Compound AH2), lithium diethoxyphosphoryl sulfate (Compound AH8),lithium dibutoxyphosphoryl sulfate (Compound AH10), and lithiumdifluorophosphoryl sulfate (Compound AH15) are more preferred.

In the nonaqueous electrolytic solution of the present invention, acontent of the SO₄ group-containing compound represented by theforegoing general formula (I-2), which is contained in the nonaqueouselectrolytic solution, is preferably 0.001% to 5% by mass in thenonaqueous electrolytic solution. So long as the content is 5% by massor less, there is less concern that a surface film is excessively formedon the electrode, thereby worsening the low-temperature properties, andso long as the content is 0.001% by mass or more, the formation of asurface film is satisfactory, and the effect for improvinghigh-temperature storage properties is increased. Thus, the foregoingrange is preferred. The content is more preferably 0.05% by mass ormore, and still more preferably 0.1% by mass or more in the nonaqueouselectrolytic solution. Its upper limit is more preferably 3% by mass orless, and still more preferably 1% by mass or less.

Other suitable examples of the SO₄ group-containing compound representedby the general formula (I) include compounds represented by thefollowing general formula (I-3):

In the formula (I-3), L¹³ represents an alkyl group having 1 to 12carbon atoms, in which at least one hydrogen atom is substituted with ahalogen atom, an alkoxyalkyl group having 2 to 12 carbon atoms, in whichat least one hydrogen atom is substituted with a halogen atom, or anaryl group having 6 to 12 carbon atoms, in which at least one hydrogenatom is substituted with a halogen atom.

In the foregoing general formula (I-3), L¹³ is preferably an alkyl grouphaving 1 to 8 carbon atoms, in which at least one hydrogen atom issubstituted with a halogen atom, an alkoxyalkyl group having 2 to 8carbon atoms, in which at least one hydrogen atom is substituted with ahalogen atom, or an aryl group having 6 to 10 carbon atoms, in which atleast one hydrogen atom is substituted with a halogen atom, and morepreferably an alkyl group having 1 to 5 carbon atoms, and preferably 1to 4 carbon atoms, in which at least one hydrogen atom is substitutedwith a halogen atom, an alkoxyalkyl group having 2 to 4 carbon atoms, inwhich at least one hydrogen atom is substituted with a halogen atom, oran aryl group having 6 to 8 carbon atoms.

The halogen atom is preferably a fluorine atom.

As specific examples of L¹³, there are suitably exemplified afluoroalkyl group, such as a fluoromethyl group, a difluoromethyl group,a trifluoromethyl group, a 2-fluoroethyl group, a 2,2-difluoroethylgroup, a 2,2,2-trifluoroethyl group, a 3-fluoropropyl group, a3,3-difluoropropyl group, a 3,3,3-trifluoropropyl group, a2,2,3,3-tetrafluoropropyl group, a 2,2,3,3,3-pentafluoropropyl group, a1,1,1,3,3,3-hexafluoro-2-propyl group, etc.; a fluoroalkoxyalkyl group,such as a fluoromethoxymethyl group, a difluoromethoxymethyl group, atrifluoromethoxymethyl group, a 2-fluoroethoxymethyl group, a2,2-difluoroethoxymethyl group, a 2,2,2-trifluoroethoxymethyl group, afluoromethoxyethyl group, a difluoromethoxyethyl group, atrifluoromethoxyethyl group, a 2-fluoroethoxyethyl group, a2,2-difluoroethoxyethyl group, a 2,2,2-trifluoroethoxymethyl group,etc.; and an aryl group, such as a 2-fluorophenyl group, a4-fluorophenyl group, a 4-trifluoromethylphenyl group, a2,4-difluorophenyl group, a perfluorophenyl group, etc. Above all, atrifluoromethyl group, a 2,2,2-trifluoroethyl group, a2,2,3,3,3-pentafluoropropyl group, a fluoromethoxyethyl group, a2,2,2-trifluoroethoxymethyl group, a 4-fluorophenyl group, and aperfluorophenyl group are preferred; and a 2,2,2-trifluoroethyl group, a2,2,3,3-tetrafluoropropyl group, and a 4-fluorophenyl group are morepreferred.

Specifically, examples of the SO₄ group-containing compound representedby the foregoing general formula (I-3) include the following compounds.

There are suitably exemplified lithium fluoromethyl sulfate, lithiumdifluoromethyl sulfate, lithium trifluoromethyl sulfate, lithium2-fluoroethyl sulfate, lithium 2,2-difluoroethyl sulfate, lithium2,2,2-trifluoroethyl sulfate, lithium 3-fluoropropyl sulfate, lithium3,3-difluoropropyl sulfate, lithium 3,3,3-trifluoropropyl sulfate,lithium 2,2,3,3-tetrafluoropropyl sulfate, lithium2,2,3,3,3-pentafluoropropyl sulfate, lithium1,1,1,3,3,3-hexafluoro-2-propyl sulfate, lithium fluoromethoxymethylsulfate, lithium difluoromethoxymethyl sulfate, lithiumtrifluoromethoxymethyl sulfate, lithium 2-fluoroethoxymethyl sulfate,lithium 2,2-difluoroethoxymethyl sulfate, lithium2,2,2-trifluoroethoxymethyl sulfate, lithium fluoromethoxyethyl sulfate,lithium difluoromethoxyethyl sulfate, lithium trifluoromethoxyethylsulfate, lithium 2-fluoroethoxyethyl sulfate, lithium2,2-difluoroethoxyethyl sulfate, lithium 2,2,2-trifluoroethoxyethylsulfate, lithium 2-fluorophenyl sulfate, lithium 4-fluorophenyl sulfate,lithium 4-trifluoromethylphenyl sulfate, lithium 2,4-difluorophenylsulfate, and lithium perfluorophenyl sulfate.

Among the SO₄ group-containing compounds represented by the foregoinggeneral formula (I-3), one or more selected from lithium trifluoromethylsulfate, lithium 2,2,2-trifluoroethyl sulfate, lithium2,2,3,3-tetrafluoropropyl sulfate, lithium1,1,1,3,3,3-hexafluoro-2-propyl sulfate, lithium 4-fluorophenyl sulfate,and lithium perfluorophenyl sulfate are more preferred.

A concentration of the SO₄ group-containing compound represented by theforegoing general formula (I-3) in the nonaqueous electrolytic solutionis preferably 5% by mass or more, and more preferably 5.5% by mass ormore. Its upper limit is preferably 25% by mass or less, more preferably20% by mass or less, and still more preferably 13% by mass or less.

[SO₄ Group-Containing Compounds Represented by the General Formula (II)]

wherein L² represents a p-valent hydrocarbon connecting group which maycontain an ether bond, a thioether bond, or an —S(═O)₂ bond, and p is aninteger of 2 to 4, provided that at least one hydrogen atom which L² hasmay be substituted with a halogen atom.

In the foregoing general formula (II), p is preferably 2 or 3, and morepreferably 2.

Specific examples of L² include the following connecting groups.

(i) Connecting Group in the Case of p=2:

There are suitably exemplified a straight-chain alkylene group, such asan ethylene group, a propane-1,3-diyl group, a butane-1,4-diyl group, apentane-1,5-diyl group, a hexane-1,6-diyl group, etc.; a branchedalkylene group, such as a propane-1,2-diyl group, a butane-1,3-diylgroup, a butane-2,3-diyl group, a 2-methylpropane-1,2-diyl group, a2,2-dimethylpropane-1,3-diyl group, etc.; a haloalkylene group, such asa 2,2-difluoropropane-1,3-diyl group, a2,2,3,3-tetrafluorobutane-1,4-diyl group, a2,2,3,3,4,4-hexafluoropentane-1,5-diyl group, a2,2,3,3,4,4,5,5-octafluorohexane-1,6-diyl group, a2,2-dichloropropane-1,3-diyl group, a 2,2,3,3-tetrachlorobutane-1,4-diylgroup, etc.; an alkenylene group, such as a 2-butene-1,4-diyl group, a2-pentene-1,5-diyl group, a 3-hexene-1,6-diyl group, a 3-hexene-2,5-diylgroup, a 2,5-dimethyl-3-hexene-2,5-diyl group, etc.; an alkynylenegroup, such as a 2-butyne-1,4-diyl group, a 2-pentyne-1,5-diyl group, a3-hexyne-1,6-diyl group, a 3-hexyne-2,5-diyl group, a2,5-dimethyl-3-hexyne-2,5-diyl group, etc.; a cycloalkylene group, suchas a cyclopentane-1,2-diyl group, a cyclopentane-1,3-diyl group, acyclohexane-1,2-diyl group, a cyclohexane-1,4-diyl group, acycloheptane-1,2-diyl group, a cycloheptane-1,4-diyl group, acyclooctane-1,2-diyl group, a cyclooctane-1,5-diyl group, etc.; aconnecting group having an ether bond, such as —CH₂CH₂OCH₂CH₂—,—CH₂CH₂OCH₂CH₂OCH₂CH₂—, —CH₂CH₂CH₂OCH₂CH₂CH₂—, —CH(CH₃)CH₂OCH₂CH(CH₃)—,etc.; a connecting group having a thioether bond, such as—CH₂CH₂SCH₂CH₂—, —CH₂CH₂CH₂SCH₂CH₂CH₂—, etc.; a connecting group havingan S(═O)₂ bond, such as —CH₂CH₂S(—O)₂CH₂CH₂—,—CH₂CH₂CH₂S(—O)₂CH₂CH₂CH₂—, etc.; and an aromatic connecting group, suchas a benzene-1,2-diyl group, a benzene-1,3-diyl group, abenzene-1,4-diyl group, etc.

(ii) The Case of p=3:

There are suitably exemplified connecting groups having the followingstructures.

(iii) The Case of p=4:

There are suitably exemplified connecting groups having the followingstructures.

In L², an ethylene group, a propane-1,3-diyl group, a butane-1,4-diylgroup, a pentane-1,5-diyl group, a hexane-1,6-diyl group, apropane-1,2-diyl group, a butane-1,3-diyl group, a butane-2,3-diylgroup, a 2,2-dimethylpropane-1,3-diyl group, a2,2-difluoropropane-1,3-diyl group, a 2,2,3,3-tetrafluorobutane-1,4-diylgroup, a 2,2,3,3,4,4-hexafluoropentane-1,5-diyl group, a2-butene-1,4-diyl group, a 3-hexene-2,5-diyl group, a 2-butyne-1,4-diylgroup, a 3-hexyne-2,5-diyl group, a cyclohexane-1,2-diyl group, acyclohexane-1,4-diyl group, a cycloheptane-1,2-diyl group,—CH₂CH₂OCH₂CH₂—, —CH₂CH₂OCH₂CH₂OCH₂CH₂—, —CH₂CH₂S(═O)₂CH₂CH₂—, and abenzene-1,4-diyl group are preferred; and an ethylene group, apropane-1,3-diyl group, a butane-1,4-diyl group, a propane-1,2-diylgroup, a butane-1,3-diyl group, a butane-2,3-diyl group, a2,2-dilfuoropropane-1,3-diyl group, a 2,2,3,3-tetrafluorobutane-1,4-diylgroup, a 2-butene-1,4-diyl group, a 2-butyne-1,4-diyl group, acyclohexane-1,4-diyl group, —CH₂CH₂OCH₂CH₂—, and —CH₂CH₂S(═O)₂CH₂CH₂—are more preferred.

Specifically, examples of the SO₄ group-containing compound representedby the foregoing general formula (II) include the following compounds.

(A) Suitable Compounds in the Case of p=2:

(B) Suitable Compounds in the Case of p=3:

(C) Suitable Compounds in the Case of p=4:

Among the SO₄ group-containing compounds represented by the foregoinggeneral formula (II), one or more selected from Compounds BA1 to BAB,BA10 to BA13, BA17, BA20, BA22, BA29, BA31 to BA34, BA39, and BA43 toBA46 are preferred; and one or more selected from lithiumethane-1,2-diyl bis(sulfate) (Compound BA1), lithium propane-1,3-diylbis(sulfate) (Compound BA2), lithium butane-1,4-diyl bis(sulfate)(Compound BA3), lithium pentane-1,5-diyl bis(sulfate) (Compound BA4),lithium hexane-1,6-diyl bis(sulfate) (Compound BA5), lithiumpropane-1,2-diyl bis(sulfate) (Compound BA6), lithium butane-1,3-diylbis(sulfate) (Compound BA7), lithium butane-2,3-diyl bis(sulfate)(Compound BA8), lithium 2,2-difluoropropane-1,3-diyl bis(sulfate)(Compound BA11), lithium 2,2,3,3-tetrafluorobutane-1,4-diyl bis(sulfate)(Compound BA12), lithium 2-butene-1,4-diyl bis(sulfate) (Compound BA17),lithium 2-butyne-1,4-diyl bis(sulfate) (Compound BA22), lithiumcyclohexane-1,4-diyl bis(sulfate) (Compound BA31), lithiumoxybis(ethane-2,1-diyl)bis(sulfate) (Compound BA33), and lithiumsulfonylbis(ethane-2,1-diyl)bis(sulfate) (Compound BA39) are morepreferred.

In the nonaqueous electrolytic solution of the present invention, acontent of the SO₄ group-containing compound represented by theforegoing general formula (II), which is contained in the nonaqueouselectrolytic solution, is preferably 0.001% to 5% by mass in thenonaqueous electrolytic solution. So long as the content is 5% by massor less, there is less concern that a surface film is excessively formedon the electrode, thereby worsening the low-temperature properties, andso long as the content is 0.001% by mass or more, the formation of asurface film is satisfactory, and the effect for improvinghigh-temperature storage properties is increased. Thus, the foregoingrange is preferred. The content is more preferably 0.05% by mass ormore, and still more preferably 0.1% by mass or more in the nonaqueouselectrolytic solution. Its upper limit is more preferably 3% by mass orless, and still more preferably 1% by mass or less.

[SO₄ Group-Containing Compounds Represented by the General Formula(III)]

wherein each of R³¹ to R³³ independently represents an alkyl grouphaving 1 to 12 carbon atoms, an alkenyl group having 2 to 3 carbonatoms, or an aryl group having 6 to 8 carbon atoms, and q is an integerof 1 to 4,

when q is 1, then R³¹ may be —OSO₃—R³⁷, and R³⁷ is synonymous with R³¹.

when q is 1, then L³ represents an alkyl group having 1 to 12 carbonatoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl grouphaving 3 to 6 carbon atoms, an alkoxyalkyl group having 2 to 12 carbonatoms, a —CR³⁴R³⁵C(═O)OR³⁶ group, or an aryl group having 6 to 12 carbonatoms, and when q is 2 to 4, then L³ represents a q-valent hydrocarbonconnecting group which may contain an ether bond, a thioether bond, oran —S(═O)₂— bond,

each of R³⁴ and R³⁵ independently represents a hydrogen atom, a halogenatom, or an alkyl group having 1 to 4 carbon atoms, and R³⁶ representsan alkyl group having 1 to 8 carbon atoms, an alkenyl group having 2 to6 carbon atoms, or an alkynyl group having 3 to 6 carbon atoms, and

in each of the alkyl group and the aryl group represented by L³, and thealkyl group represented by each of R³⁴ to R³⁶, at least one hydrogenatom may be substituted with a halogen atom.

Suitable examples of the SO₄ group-containing compound represented bythe general formula (III) include compounds represented by the followinggeneral formula (III-1):

wherein L³¹ represents an alkyl group having 1 to 12 carbon atoms, analkenyl group having 2 to 6 carbon atoms, an alkynyl group having 3 to 6carbon atoms, an alkoxyalkyl group having 2 to 12 carbon atoms, a—CR³⁴R³⁵C(═O)OR³⁶ group, or an aryl group having 6 to 12 carbon atoms,and R³¹ to R³³ and R³⁴ to R³⁶ are the same as those described above, andin each of the alkyl group and the aryl group represented by L³¹, atleast one hydrogen atom may be substituted with a halogen atom.

In the foregoing general formula (III-1), L³¹ is preferably an alkylgroup having 1 to 8 carbon atoms, an alkenyl group having 3 to 4 carbonatoms, an alkynyl group having 3 to 4 carbon atoms, an alkoxyalkyl grouphaving 2 to 8 carbon atoms, a —CR³⁴R³⁵C(═O)OR³⁶ group, or an aryl grouphaving 6 to 10 carbon atoms, and more preferably an alkyl group having 1to 5 carbon atoms, and preferably 1 to 4 carbon atoms, in which at leastone hydrogen atom may be substituted with a halogen atom, an alkenylgroup having 3 carbon atoms, an alkynyl group having 3 carbon atoms, analkoxyalkyl group having 2 to 4 carbon atoms, a —CR³⁴R³⁵C(═O)OR³⁶ group,or an aryl group having 6 to 8 carbon atoms.

In the case where L³¹ is a group other than the —CR³⁴R³⁵C(═O)OR³⁶ group,as specific examples thereof, there are suitably exemplified astraight-chain alkyl group, such as a methyl group, an ethyl group, ann-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group,an n-heptyl group, an n-octyl group, an n-decyl group, an n-dodecylgroup, etc.; a branched alkyl group, such as an isopropyl group, asec-butyl group, a tert-butyl group, a tert-amyl group, a 2-ethylhexylgroup, etc.; a cycloalkyl group, such as a cyclopentyl group, acyclohexyl group, etc.; a fluoroalkyl group, such as a fluoromethylgroup, a difluoromethyl group, a trifluoromethyl group, a 2-fluoroethylgroup, a 2,2-difluoroethyl group, a 2,2,2-trifluoroethyl group, a3-fluoropropyl group, a 3,3-difluoropropyl group, a3,3,3-trifluoropropyl group, a 2,2,3,3-tetrafluoropropyl group, a2,2,3,3,3-pentafluoropropyl group, etc.; a straight-chain alkenyl group,such as a vinyl group, a 2-propenyl group, a 2-butenyl group, a3-butenyl group, etc.; a branched alkenyl group, such as a2-methyl-2-propenyl group, etc.; a straight-chain alkynyl group, such asa 2-propynyl group, a 2-butynyl group, a 3-butynyl group, a 4-pentynylgroup, a 5-hexynyl group, etc.; a branched alkynyl group, such as a1-methyl-2-propynyl group, a 1-methyl-2-butynyl group, a1,1-dimethyl-2-propynyl group, etc.; an alkoxyalkyl group, such as amethoxymethyl group, an ethoxymethyl group, a methoxyethyl group, anethoxyethyl group, an n-propoxyethyl group, an n-butoxyethyl group, ann-hexyloxyethyl group, a methoxypropyl group, an ethoxypropyl group,etc.; and an aryl group, such as a phenyl group, a 2-methylphenyl group,a 3-methylphenyl group, a 4-methylphenyl group, a 4-tert-butylphenylgroup, a 2-fluorophenyl group, a 4-fluorophenyloxy group, a4-trifluoromethylphenyl group, a 2,4-difluorophenyl group, aperfluorophenyl group, etc.

Among the foregoing, a methyl group, an ethyl group, an n-propyl group,an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptylgroup, an n-octyl group, an isopropyl group, a sec-butyl group, atrifluoromethyl group, a 2,2,2-trifluoroethyl group, a2,2,3,3-tetrafluoropropyl group, a methoxyethyl group, an ethoxyethylgroup, an n-propoxyethyl group, an n-butoxyethyl group, ann-hexyloxyethyl group, a methoxypropyl group, an ethoxypropyl group, avinyl group, a 2-propenyl group, a 2-butenyl group, a2-methyl-2-propenyl group, a 2-propynyl group, a 2-butynyl group, a3-butynyl group, a 1-methyl-2-propynyl group, a phenyl group, a4-methylphenyl group, a 4-fluorophenyl group, and a perfluorophenylgroup are preferred; and a methyl group, an ethyl group, an n-propylgroup, an n-butyl group, an isopropyl group, a 2,2,2-trifluoroethylgroup, a 2,2,3,3-tetrafluoropropyl group, a 2-propenyl group, a2-propynyl group, a methoxyethyl group, a methoxypropyl group, a phenylgroup, and a 4-fluorophenyl group are more preferred.

In the case where L³¹ is a —CR³⁴R³⁵C(═O)OR³⁶ group, each of R³⁴ and R³⁵is preferably a hydrogen atom or an alkyl group having 1 to 3 carbonatoms, in which at least one hydrogen atom may be substituted with ahalogen atom, and more preferably a hydrogen atom or an alkyl grouphaving 1 carbon atom.

As specific examples of R³⁴ and R³⁵, there are suitably exemplified ahydrogen atom; a halogen atom, such as a fluorine atom, a chlorine atom,etc.; a straight-chain alkyl group, such as a methyl group, an ethylgroup, an n-propyl group, an n-butyl group, etc.; a branched alkylgroup, such as an isopropyl group, a sec-butyl group, a tert-butylgroup, etc.; and a halogen atom-substituted alkyl group, such as afluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a2-fluoroethyl group, a 2,2-difluoroethyl group, a 2,2,2-trifluoroethylgroup, a 3-fluoropropyl group, a 3,3-difluoropropyl group, a3,3,3-trifluoropropyl group, a 2,2,3,3-tetrafluoropropyl group, a2,2,3,3,3-pentafluoropropyl group, etc. Above all, a hydrogen atom, afluorine atom, a methyl group, an ethyl group, an n-propyl group, and ann-butyl group are more preferred; and a hydrogen atom and a methyl groupare still more preferred.

In the —CR³⁴R³⁵C(═O)OR³⁶ group, R³⁶ is preferably an alkyl group having1 to 3 carbon atoms, in which at least one hydrogen atom may besubstituted with a halogen atom, an alkenyl group having 2 to 4 carbonatoms, or an alkynyl group having 3 to 4 carbon atoms.

As specific examples of R³⁶, there are suitably exemplified astraight-chain alkyl group, such as a methyl group, an ethyl group, ann-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group,an n-heptyl group, an n-octyl group, etc.; a branched alkyl group, suchas an isopropyl group, a sec-butyl group, a tert-butyl group, atert-amyl group, a 2-ethylhexyl group, etc.; a cycloalkyl group, such asa cyclopentyl group, a cyclohexyl group, etc.; an alkyl group in whichat least one hydrogen atom is substituted with a halogen group, such asa fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a2-fluoroethyl group, a 2,2-difluoroethyl group, a 2,2,2-trifluoroethylgroup, a 3-fluoropropyl group, a 3,3-difluoropropyl group, a3,3,3-trifluoropropyl group, a 2,2,3,3-tetrafluoropropyl group, a2,2,3,3,3-pentafluoropropyl group, etc.; a straight-chain alkenyl group,such as a vinyl group, a 2-propenyl group, a 2-butenyl group, a3-butenyl group, etc.; a branched alkenyl group, such as a2-methyl-2-propenyl group, etc.; a straight-chain alkynyl group, such asa 2-propynyl group, a 2-butynyl group, a 3-butynyl group, a 4-pentynylgroup, a 5-hexynyl group, etc.; and a branched alkynyl group, such as a1-methyl-2-propynyl group, a 1-methyl-2-butynyl group, a1,1-dimethyl-2-propynyl group, etc. Above all, a methyl group, an ethylgroup, an n-propyl group, an n-butyl group, a 2-fluoroethyl group, a2,2,2-trifluoroethyl group, a 2,2,3,3-tetrafluoropropyl group, a2-propenyl group, a 2-butenyl group, a 2-propynyl group, and a 2-butynylgroup are more preferred; and a methyl group, an ethyl group, a2,2,2-trifluoroethyl group, a 2,2,3,3-tetrafluoropropyl group, a2-propenyl group, and a 2-propynyl group are still more preferred.

In the case where L³¹ is a —CR³⁴R³⁵C(═O)OR³⁶ group, as specific examplesthereof, there are suitably exemplified the following groups.

In L³¹, the following groups are more preferred.

In the general formula (III-1), each of R³¹ to R³³ independentlyrepresents an alkyl group having 1 to 12 carbon atoms, an alkenyl grouphaving 2 to 3 carbon atoms, or an aryl group having 6 to 8 carbon atoms,preferably an alkyl group having 1 to 4 carbon atoms, an alkenyl grouphaving 2 carbon atoms, or an aryl group having 6 to 7 carbon atoms, morepreferably an alkyl group having 1 to 2 carbon atoms or an aryl grouphaving 6 carbon atoms, and still more preferably an alkyl group having 1carbon atom.

As specific examples of R³¹ to R³³, there are suitably exemplified astraight-chain alkyl group, such as a methyl group, an ethyl group, ann-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group,an n-heptyl group, an n-octyl group, an n-decyl group, an n-dodecylgroup, etc.; a branched alkyl group, such as an isopropyl group, asec-butyl group, a tert-butyl group, a tert-amyl group, a 2-ethylhexylgroup, etc.; a cycloalkyl group, such as a cyclopentyl group, acyclohexyl group, etc.; an alkenyl group, such as a vinyl group, a2-propenyl group, etc.; an aryl group, such as a phenyl group, a2-methylphenyl group, a 3-methylphenyl group, a 4-methylphenyl group, a4-tert-butylphenyl group, a 2-fluorophenyl group, a 4-fluorophenylgroup, a 4-trifluoromethylphenyl group, a 2,4-difluorophenyl group, aperfluorophenyl group, etc.; and the like.

Above all, a methyl group, an ethyl group, an n-propyl group, an n-butylgroup, an isopropyl group, a sec-butyl group, a tert-butyl group, avinyl group, a phenyl group, a 4-methylphenyl group, a 4-fluorophenylgroup, and a perfluorophenyl group are more preferred; and a methylgroup is still more preferred.

R³¹ to R³³ may be bonded to each other to form a ring.

Specifically, as the SO₄ group-containing compound represented by theforegoing general formula (III-1), there are suitably exemplified thefollowing compounds.

Among the SO₄ group-containing compounds represented by the foregoinggeneral formula (III-1), Compounds CA1 to CA16, CA18 to CA20, and CA23to CA51 are preferred; Compounds CA1, CA10 to CA16, CA18 to CA20, CA23to CA40, and CA50 to CA51 are more preferred; and one or more selectedfrom methyl trimethylsilyl sulfate (Compound CA1), ethyl trimethylsilylsulfate (Compound CA10), n-propyl trimethylsilyl sulfate (CompoundCA11), n-butyl trimethylsilyl sulfate (Compound CA12), isopropyltrimethylsilyl sulfate (Compound CA18), 2,2,2-trifluoroethyltrimethylsilyl sulfate (Compound CA23), 2,2,3,3-tetrafluoropropyltrimethylsilyl sulfate (Compound CA24), methoxyethyl trimethylsilylsulfate (Compound CA25), methoxypropyl trimethylsilyl sulfate (CompoundCA28), allyl trimethylsilyl sulfate (Compound CA30), 2-propynyltrimethylsilyl sulfate (Compound CA33), phenyl trimethylsilyl sulfate(Compound CA37), 4-fluorophenyl trimethylsilyl sulfate (Compound CA39),pentafluorophenyl trimethylsilyl sulfate (Compound CA40), trimethylsilyl1-(methoxycarbonyl)ethyl sulfate (Compound CA50), and trimethylsilyl1-(2-propynyloxycarbonyl)ethyl sulfate (Compound CA51) are still morepreferred.

Suitable examples of the SO₄ group-containing compound represented bythe general formula (III) include compounds represented by the followinggeneral formula (III-2):

wherein each of R³¹ to R³³ independently represents an alkyl grouphaving 1 to 12 carbon atoms, an alkenyl group having 2 to 3 carbonatoms, or an aryl group having 6 to 8 carbon atoms, and may be bonded toeach other to form a ring,

L³² represents a q-valent hydrocarbon connecting group, and q is aninteger of 2 to 4, provided that L³² may contain an ether bond, athioether bond, or an SO₂ bond, and at least one hydrogen atom may besubstituted with a halogen atom, and

q is preferably 2 or 3, and more preferably 2.

In the general formula (III-2), each of R³¹ to R³³ independentlyrepresents an alkyl group having 1 to 12 carbon atoms, an alkenyl grouphaving 2 to 3 carbon atoms, or an aryl group having 6 to 8 carbon atoms,preferably an alkyl group having 1 to 4 carbon atoms, an alkenyl grouphaving 2 carbon atoms, or an aryl group having 6 to 7 carbon atoms, morepreferably an alkyl group having 1 to 2 carbon atoms or an aryl grouphaving 6 carbon atoms, and still more preferably an alkyl group having 1carbon atom.

As specific examples of R³¹ to R³³, there are suitably exemplified astraight-chain alkyl group, such as a methyl group, an ethyl group, ann-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group,an n-heptyl group, an n-octyl group, an n-decyl group, an n-dodecylgroup, etc.; a branched alkyl group, such as an isopropyl group, asec-butyl group, a tert-butyl group, a tert-amyl group, a 2-ethylhexylgroup, etc.; a cycloalkyl group, such as a cyclopentyl group, acyclohexyl group, etc.; an alkenyl group, such as a vinyl group, a2-propenyl group, etc.; an aryl group, such as a phenyl group, a2-methylphenyl group, a 3-methylphenyl group, a 4-methylphenyl group, a4-tert-butylphenyl group, a 2-fluorophenyl group, a 4-fluorophenylgroup, a 4-trifluoromethylphenyl group, a 2,4-difluorophenyl group, aperfluorophenyl group, etc.; and the like.

Above all, one or more selected from a methyl group, an ethyl group, ann-propyl group, an n-butyl group, an isopropyl group, a sec-butyl group,a tert-butyl group, a vinyl group, a phenyl group, a 4-methylphenylgroup, a 4-fluorophenyl group, and a perfluorophenyl group are morepreferred; and a methyl group is still more preferred.

Specific examples of L³² include the following connecting groups.

(i) Connecting Group in the Case of q=2:

There are suitably exemplified a straight-chain alkylene group, such asan ethylene group, a propane-1,3-diyl group, a butane-1,4-diyl group, apentane-1,5-diyl group, a hexane-1,6-diyl group, etc.; a branchedalkylene group, such as a propane-1,2-diyl group, a butane-1,3-diylgroup, a butane-2,3-diyl group, a 2-methylpropane-1,2-diyl group, a2,2-dimethylpropane-1,3-diyl group, etc.; a haloalkyl group, such as a2,2-difluoropropane-1,3-diyl group, a 2,2,3,3-tetrafluorobutane-1,4-diylgroup, a 2,2,3,3,4,4-hexafluoropentane-1,5-diyl group, a2,2,3,3,4,4,5,5-octafluorohexane-1,6-diyl group, a2,2-dichloropropane-1,3-diyl group, a 2,2,3,3-tetrachlorobutane-1,4-diylgroup, etc.; an alkenylene group, such as a 2-butene-1,4-diyl group, a2-pentene-1,5-diyl group, a 3-hexene-1,6-diyl group, a 3-hexene-2,5-diylgroup, a 2,5-dimethyl-3-hexene-2,5-diyl group, etc.; an alkynylenegroup, such as a 2-butyne-1,4-diyl group, a 2-pentyne-1,5-diyl group, a3-hexyne-1,6-diyl group, a 3-hexyne-2,5-diyl group, a2,5-dimethyl-3-hexyne-2,5-diyl group, etc.; a cycloalkylene group, suchas a cyclopentane-1,2-diyl group, a cyclopentane-1,3-diyl group, acyclohexane-1,2-diyl group, a cyclohexane-1,4-diyl group, acycloheptane-1,2-diyl group, a cycloheptane-1,4-diyl group, acyclooctane-1,2-diyl group, a cyclooctane-1,5-diyl group, etc.; aconnecting group having an ether bond, such as —CH₂CH₂OCH₂CH₂—,—CH₂CH₂OCH₂CH₂OCH₂CH₂—, —CH₂CH₂OCH₂CH₂OCH₂CH₂OCH₂CH₂—,—CH₂CH₂CH₂OCH₂CH₂CH₂—, etc.; a connecting group having a thioether bond,such as —CH₂CH₂SCH₂CH₂—, —CH₂CH₂CH₂SCH₂CH₂CH₂—, etc.; a connecting grouphaving an S(═O)₂ bond, such as —CH₂CH₂S(—O)₂CH₂CH₂—,—CH₂CH₂CH₂S(—O)₂CH₂CH₂CH₂—, etc.; and an aromatic connecting group, suchas a benzene-1,2-diyl group, a benzene-1,3-diyl group, abenzene-1,4-diyl group, etc.

(ii) The Case of q=3:

There are suitably exemplified connecting groups having the followingstructures.

(iii) The Case of q=4:

There are suitably exemplified connecting groups having the followingstructures.

In L³², an ethylene group, a propane-1,3-diyl group, a butane-1,4-diylgroup, a pentane-1,5-diyl group, a hexane-1,6-diyl group, apropane-1,2-diyl group, a butane-1,3-diyl group, a butane-2,3-diylgroup, a 2,2-dimethylpropane-1,3-diyl group, a2,2-difluoropropane-1,3-diyl group, a 2,2,3,3-tetrafluorobutane-1,4-diylgroup, a 2,2,3,3,4,4-hexafluoropentane-1,5-diyl group, a2-butene-1,4-diyl group, a 3-hexene-2,5-diyl group, a 2-butyne-1,4-diylgroup, a 3-hexyne-2,5-diyl group, a cyclohexane-1,2-diyl group, acyclohexane-1,4-diyl group, a cycloheptane-1,2-diyl group,—CH₂CH₂OCH₂CH₂—, —CH₂CH₂OCH₂CH₂OCH₂CH₂—, —CH₂CH₂S(═O)₂CH₂CH₂—, and abenzene-1,4-diyl group are preferred; and an ethylene group, apropane-1,3-diyl group, a butane-1,4-diyl group, a propane-1,2-diylgroup, a butane-1,3-diyl group, a butane-2,3-diyl group, a2,2-dilfuoropropane-1,3-diyl group, a 2,2,3,3-tetrafluorobutane-1,4-diylgroup, a 2-butene-1,4-diyl group, a 2-butyne-1,4-diyl group, acyclohexane-1,4-diyl group, —CH₂CH₂OCH₂CH₂—, and —CH₂CH₂S(═O)₂CH₂CH₂—are more preferred.

Specifically, examples of the SO₄ group-containing compound representedby the foregoing general formula (III-2) include the followingcompounds.

[a] The case of q=2:

[b] The case of q=3:

[c] The case of q=4:

Among the compounds represented by the foregoing general formula(III-2), one or more selected from Compounds CE1 to CE8, CE10 to CE13,CE17, CE20, CE22, CE29, CE31 to CE34, CE39, and CE43 to CE46 arepreferred; and one or more selected from ethane-1,2-diylbis(trimethylsilyl)bis(sulfate) (Compound CE1), propane-1,3-diylbis(trimethylsilyl)bis(sulfate) (Compound CE2), butane-1,4-diylbis(trimethylsilyl)bis(sulfate) (Compound CE3), pentane-1,5-diylbis(trimethylsilyl)bis(sulfate) (Compound CE4), hexane-1,6-diylbis(trimethylsilyl)bis(sulfate) (Compound CE5), propane-1,2-diylbis(trimethylsilyl)bis(sulfate) (Compound CE6), butane-1,3-diylbis(trimethylsilyl)bis(sulfate) (Compound CE7), butane-2,3-diylbis(trimethylsilyl)bis(sulfate) (Compound CE8),2,2-difluoropropane-1,3-diyl bis(trimethylsilyl)bis(sulfate) (CompoundCE11), 2,2,3,3-tetrafluorobutane-1,4-diylbis(trimethylsilyl)bis(sulfate) (Compound CE12), 2-butene-1,4-diylbis(trimethylsilyl)bis(sulfate) (Compound CE17), 2-butyne-1,4-diylbis(trimethylsilyl)bis(sulfate) (Compound CE22), cyclohexane-1,4-diylbis(trimethylsilyl)bis(sulfate) (Compound CE31),oxybis(ethane-2,1-diyl)bis(trimethylsilyl) bis(sulfate) (Compound CE33),and sulfonyl bis(ethane-2,1-diyl)bis(trimethylsilyl) bis(sulfate)(Compound CE39) are more preferred.

In the nonaqueous electrolytic solution of the present invention, acontent of the compound represented by the foregoing general formula(III), (III-1), or (III-2), which is contained in the nonaqueouselectrolytic solution, is preferably 0.001% to 5% by mass in thenonaqueous electrolytic solution. So long as the content is 5% by massor less, there is less concern that a surface film is excessively formedon the electrode, thereby worsening the low-temperature properties, andso long as the content is 0.001% by mass or more, the formation of asurface film is satisfactory, and the effect for improvinghigh-temperature storage properties is increased. Thus, the foregoingrange is preferred. The content is more preferably 0.05% by mass ormore, and still more preferably 0.1% by mass or more in the nonaqueouselectrolytic solution. Its upper limit is more preferably 3% by mass orless, and still more preferably 1% by mass or less.

[SO₄ Group-Containing Compounds Represented by the General Formula (IV)]

wherein L⁴ represents an alkyl group having 1 to 12 carbon atoms, analkenyl group having 2 to 6 carbon atoms, an alkynyl group having 3 to 6carbon atoms, an alkoxyalkyl group having 2 to 12 carbon atoms, a—CR⁴¹R⁴²C(═O)OR⁴³ group, or an aryl group having 6 to 12 carbon atoms, Xrepresents an SiR⁴⁴R⁴⁵ group, a quaternary onium, an alkali metalbelonging to the third or fourth period of the Periodic Table, or analkaline earth metal belonging to the third or fourth period of thePeriodic Table, and r is an integer of 1 or 2,

provided that when X is a quaternary onium or an alkali metal belongingto the third or fourth period of the Periodic Table, then r is 1, andwhen X is an SiR⁴⁴R⁴⁵ group or an alkaline earth metal belonging to thethird or fourth period of the Periodic Table, then r is 2,

each of R⁴¹ and R⁴² independently represents a hydrogen atom, a halogenatom, or an alkyl group having 1 to 4 carbon atoms, R⁴³ represents analkyl group having 1 to 8 carbon atoms, an alkenyl group having 2 to 6carbon atoms, or an alkynyl group having 3 to 6 carbon atoms, and eachof R⁴⁴ and R⁴⁵ independently represents an alkyl group having 1 to 12carbon atoms, an alkenyl group having 2 to 3 carbon atoms, or an arylgroup having 6 to 8 carbon atoms, and

in each of the alkyl group and the aryl group, at least one hydrogenatom may be substituted with a halogen atom.

In the foregoing general formula (IV), L⁴ is preferably an alkyl grouphaving 1 to 8 carbon atoms, an alkenyl group having 3 to 4 carbon atoms,an alkynyl group having 3 to 4 carbon atoms, an alkoxyalkyl group having2 to 8 carbon atoms, a —CR⁴¹R⁴²C(═O)OR⁴³ group, or an aryl group having6 to 10 carbon atoms, and more preferably an alkyl group having 1 to 4carbon atoms, in which at least one hydrogen atom may be substitutedwith a halogen atom, an alkenyl group having 3 carbon atoms, an alkynylgroup having 3 carbon atoms, an alkoxyalkyl group having 2 to 4 carbonatoms, a —CR⁴¹R⁴²C(═O)OR⁴³ group, or an aryl group having 6 to 8 carbonatoms.

Specific examples and suitable examples in the case where L⁴ is a groupother than the —CR⁴¹R⁴²C(═O)OR⁴³ group are basically the same as thespecific examples and suitable examples in the case where L³¹ is a groupother than the —CR³⁴R³⁵C(═O)OR³⁶ group, and a fluorine atom is alsopreferred.

In addition, in the case where L⁴ is a —CR⁴¹R⁴²C(═O)OR⁴³ group, each ofR⁴¹ and R⁴² is preferably a hydrogen atom or an alkyl group having 1 to3 carbon atoms, in which at least one hydrogen atom may be substitutedwith a halogen atom, and more preferably a hydrogen atom or an alkylgroup having 1 carbon atom.

Specific examples and suitable examples of R⁴¹ and R⁴² are the same asthe specific examples and suitable examples of R³⁴ and R³⁵ as describedabove in the case where L³¹ is the —CR³⁴R³⁵C(═O)OR³⁶ group.

In the —CR⁴⁴R⁴²C(═O)OR⁴³ group, R⁴³ is preferably an alkyl group having1 to 3 carbon atoms, in which at least one hydrogen atom may besubstituted with a halogen atom, an alkenyl group having 2 to 4 carbonatoms, or an alkynyl group having 3 to 4 carbon atoms.

Specific examples and suitable examples of R⁴³ are the same as thespecific examples and suitable examples of R³⁶ in the case where L³¹ isthe —CR³⁴R³⁵C(═O)OR³⁶ group.

Specific examples and suitable examples in the case where L⁴ is the—CR⁴¹R⁴²C(═O)OR⁴³ group are the same as the specific examples andsuitable examples in the case where L³¹ is the —CR³⁴R³⁵C(═O)OR³⁶ group.

(The Case where X is an SiR⁴⁴R⁴⁵ Group)

In the general formula (IV), in the case where X is an SiR⁴⁴R⁴⁵ group,each of R⁴⁴ and R⁴⁵ independently represents an alkyl group having 1 to12 carbon atoms, an alkenyl group having 2 to 3 carbon atoms, or an arylgroup having 6 to 8 carbon atoms, preferably an alkyl group having 1 to6 carbon atoms, and preferably 1 to 4 carbon atoms, an alkenyl grouphaving 2 carbon atoms, or an aryl group having 6 to 7 carbon atoms, morepreferably an alkyl group having 1 to 2 carbon atoms or an aryl grouphaving 6 carbon atoms, and still more preferably an alkyl group having 1carbon atom.

Specific examples and suitable examples of R⁴⁴ and R⁴⁵ are the same asthe specific examples and suitable examples of R³¹ to R³³ as describedabove. R⁴⁴ and R⁴⁵ may be bonded to each other to form a ring.

In the case where X is an SiR⁴⁴R⁴⁵ group, specifically, as the SO₄group-containing compound represented by the foregoing general formula(IV), there are suitably exemplified the following compounds.

Among the aforementioned SO₄ group-containing compounds, Compounds DA52to DA66, DA68 to DA70, and DA73 to DA89 are preferred; Compounds DA52,DA62 to DA66, and DA73 to DA89 are more preferred; and one or moreselected from bis(methoxysulfonyloxy)dimethylsilane (Compound DA52),bis(ethoxysulfonyloxy)dimethylsilane (Compound DA62),bis(n-propyloxysulfonyloxy)dimethylsilane (Compound DA63),bis(n-butyloxysulfonyloxy)dimethylsilane (Compound DA64),bis(isopropyloxysulfonyloxy)dimethylsilane (Compound DA68),bis(2,2,2-trifluoroethyloxysulfonyloxy)dimethylsilane (Compound DA73),bis(2,2,3,3-tetrafluoropropyloxysulfonyloxy)dimethylsilane (CompoundDA74), bis(methoxyethyloxysulfonyloxy)dimethylsilane (Compound DA75),bis(methoxypropyloxysulfonyloxy)dimethylsilane (Compound DA77),bis(allyloxysulfonyloxy)dimethylsilane (Compound DA79),bis(2-propynyloxysulfonyloxy)dimethylsilane (Compound DA82),bis(phenyloxysulfonyloxy)dimethylsilane (Compound DA86),bis(4-fluorophenyloxysulfonyloxy)dimethylsilane (Compound DA88), andbis(pentafluorophenyloxysulfonyloxy)dimethylsilane (Compound DA89) arestill more preferred.

(The Case where X is a Quaternary Onium)

In the general formula (IV), as specific examples in the case where X isa quaternary onium, there are exemplified those represented by thefollowing general formula (IV-1).

Q⁺R⁵¹R⁵²R⁵³R⁵⁴  (Iv-1)

In the general formula (IV-1), Q represents an atom belonging to thegroup 15 of the Periodic Table, and each of R⁵¹ to R⁵⁴ independentlyrepresents a hydrocarbon group having 1 to 20 carbon atoms. Each of R⁵¹to R⁵⁴ may be either an aliphatic hydrocarbon group or an aromatichydrocarbon group, and may be bonded to each other to form a ring.

Q is preferably a nitrogen atom or a phosphorus atom.

As the hydrocarbon group having 1 to 20 carbon atoms, which isrepresented by each of R⁵¹ to R⁵⁴, there are suitably exemplified analkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 1 to16 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aralkylgroup having 6 to 10 carbon atoms, and the like.

Specific examples of the alkyl group having 1 to 6 carbon atoms includea methyl group, an ethyl group, an n-propyl group, an isopropyl group,an n-butyl group, a sec-butyl group, an isobutyl group, a tert-butylgroup, and the like. Of those, a methyl group, an ethyl group, ann-propyl group, an n-butyl group, and the like are preferred.

Specific examples of the cycloalkyl group having 1 to 16 carbon atomsinclude a cyclopentyl group, a 2-methylcyclopentyl group, a3-methylcyclopentyl group, a 2-ethylcyclopentyl group, a3-ethylcyclopentyl group, a cyclohexyl group, a 2-methylcyclohexylgroup, a 3-methylcyclohexyl group, a 4-methylcyclohexyl group, a2-ethylcyclohexyl group, a 3-ethylcyclohexyl group, a 4-ethylcyclohexylgroup, a bicyclo[3,2,1]oct-1-yl group, a bicyclo[3,2,1]oct-2-yl group,and the like. Of those, a cyclopentyl group, a 2-methylcyclopentylgroup, a 3-methylcyclopentyl group, a cyclohexyl group, a2-methylcyclohexyl group, a 3-methylcyclohexyl group, a4-methylcyclohexyl group, and the like are preferred.

Specific examples of the aryl group having 6 to 10 carbon atoms includea phenyl group, a 2-methylphenyl group, a 3-methylphenyl group, a4-methylphenyl group, a 2,3-dimethylphenyl group, and the like. Ofthose, a phenyl group is preferred.

Specific examples of the aralkyl group having 6 to 10 carbon atomsinclude a phenylmethyl group, a 1-phenylethyl group, a 2-phenylethylgroup, a diphenylmethyl group, a triphenylmethyl group, and the like. Ofthose, a phenylmethyl group and a 2-phenylethyl group are preferred.

In the light of the above, preferred examples of the quaternary oniumrepresented by the foregoing general formula (IV-1) include an aliphaticlinear quaternary salt, an aliphatic cyclic ammonium, an aliphaticcyclic phosphonium, a nitrogen-containing heterocyclic aromatic cation,and the like.

As the aliphatic linear quaternary salt, a tetraalkylammonium, atetraalkylphosphonium, and the like are especially preferred.

Specific examples of the tetraalkylammonium include tetramethylammonium,ethyltrimethylammonium, diethyldimethylammonium, triethylmethylammonium,tetraethylammonium, tetra-n-butylammonium, and the like.

Specific examples of the tetraalkylphosphonium includetetramethylphosphonium, ethyltrimethylphosphonium,diethyldimethylphosphonium, triethylmethylphosphonium,tetraethylphosphonium, tetra-n-butylphosphonium, and the like.

As the aliphatic cyclic ammonium, a pyrrolidinium, a morpholinium, animidazolinium, a tetrahydropyrimidinium, a piperadinium, a piperidinium,a pyridinium, and the like are especially preferred.

Specific examples of the pyrrolidinium include N,N-dimethylpyrrolidium,N-ethyl-N-methylpyrrolidium, N,N-diethylpyrrolidium, and the like.

Specific examples of the morpholinium include N,N-dimethylmorpholinium,N-ethyl-N-methylmorpholinium, N,N-diethylmorpholinium, and the like.

Specific examples of the imidazolinium includeN,N′-dimethylimidazolinium, N-ethyl-N′-methylimidazolinium,N,N′-diethylimidazolinium, 1,2,3-trimethylimidazolinium, and the like.

Specific examples of the tetrahydropyrimidinium includeN,N′-dimethyltetrahydropyrimidinium,N-ethyl-N′-methyltetrahydropyrimidinium,N,N′-diethyltetrahydropyrimidinium,1,2,3-trimethyltetrahydropyrimidinium, and the like.

Specific examples of the piperadinium includeN,N′,N′-trimethylpiperadinium, N-ethyl-N′,N′-dimethylpiperadinium,N,N-diethyl-N′-methylpiperadinium, N,N,N′-triethylpiperadinium, and thelike.

Specific examples of the piperidinium include N,N-dimethylpiperidinium,N-ethyl-N-methylpiperidinium, N,N-diethylpiperidinium, and the like.

Specific examples of the pyridinium include N-methylpyridinium,N-ethylpyridinium, 1,2-dimethylpyrimidinium, 1,3-dimethylpyrimidinium,1,4-dimethylpyrimidinium, 1-ethyl-2-methylpyrimidinium, and the like.

In the foregoing general formula (IV), in the case where X is aquaternary onium, specifically, there are suitably exemplified thefollowing compounds.

Among the aforementioned quaternary oniums, Compounds DB4, DB7, DB9 toDB20, DB26 to DB28, DB31, DB34, DB38, DB42, DB46, DB49, and DB54 arepreferred; and one or more selected from triethylmethylammonium methylsulfate (Compound DB4), triethylmethylammonium ethyl sulfate (CompoundDB7), triethylmethylammonium isopropyl sulfate (Compound DB10),triethylmethylammonium 2,2,2-trifluoroethyl sulfate (Compound DB12),triethylmethylammonium 2,2,3,3-tetrapropyl sulfate (Compound DB13),triethylmethylammonium allyl sulfate (Compound DB15),triethylmethylammonium 2-propynyl sulfate (Compound DB16),triethylmethylammonium phenyl sulfate (Compound DB17),triethylmethylammonium fluorophenyl sulfate (Compound DB19),triethylmethylammonium pentafluorophenyl sulfate (Compound DB20),tetra-n-butylphosphonium methyl sulfate (Compound DB26), methyltri-n-butylphosphonium methyl sulfate (Compound DB27),N-methylpyridinium methyl sulfate (Compound DB49), andN,N′-dimethylimidazolium methyl sulfate (Compound DB54) are morepreferred.

(The Case where X is an Alkali Metal Belonging to the Third or FourthPeriod of the Periodic Table)

In the case where X is an alkali metal belonging to the third or fourthperiod of the Periodic Table, the SO₄ group-containing compoundrepresented by the foregoing general formula (IV) is preferably a sodiumsalt or a potassium salt, and more preferably a sodium salt. As specificexamples thereof, there are suitably exemplified the followingcompounds.

Among the aforementioned compounds, Compounds DC1 to DC8, DC13 to DC14,DC19 to DC24, DC27 to DC30, and DC33 to DC40 are preferred; and one ormore selected from sodium methyl sulfate (Compound DC1), sodium ethylsulfate (Compound DC3), sodium n-propyl sulfate (Compound DC5), sodiumn-butyl sulfate (Compound DC7), sodium isopropyl sulfate (CompoundDC13), sodium 2,2,2-trifluoroethyl sulfate (Compound DC19), sodium2,2,3,3-tetrafluoropropyl sulfate (Compound DC21), sodium allyl sulfate(Compound DC27), sodium 2-propynyl sulfate (Compound DC29), sodiumphenyl sulfate (Compound DC33), sodium 4-fluorophenyl sulfate (CompoundDC37), and sodium pentafluorophenyl sulfate (Compound DC39) are morepreferred.

(The Case where X is an Alkaline Earth Metal Belonging to the Third orFourth Period of the Periodic Table)

In the case where X is an alkaline earth metal belonging to the third orfourth period of the Periodic Table, the SO₄ group-containing compoundrepresented by the foregoing general formula (IV) is preferably amagnesium salt or a calcium salt, and more preferably a magnesium salt.As specific examples thereof, there are suitably exemplified thefollowing compounds.

Among the aforementioned SO₄ group-containing compounds, Compounds DD1to DDB, DD13 to DD16, DD19 to DD24, DD27 to DD30, and DD33 to DD40 arepreferred; and one or more selected from magnesium methyl sulfate(Compound DD1), magnesium ethyl sulfate (Compound DD3), magnesiumn-propyl sulfate (Compound DD5), magnesium n-butyl sulfate (CompoundDD7), magnesium isopropyl sulfate (Compound DD13), magnesium2,2,2-trifluoroethyl sulfate (Compound DD19), magnesium2,2,3,3-tetrafluoropropyl sulfate (Compound DD21), magnesium allylsulfate (Compound DD27), magnesium 2-propynyl sulfate (Compound DD29),magnesium phenyl sulfate (Compound DD33), magnesium 4-fluorophenylsulfate (Compound DD37), and magnesium pentafluorophenyl sulfate(Compound DD39) are more preferred.

Among the compounds represented by the foregoing general formula (IV),compounds wherein X is an SiR⁴⁴R⁴⁵ group, an alkali metal belonging tothe third or fourth period of the Periodic Table, or an alkaline earthmetal belonging to the third or fourth period of the Periodic Table aremore preferred, and compounds wherein X is an SiR⁴⁴R⁴⁵ group are stillmore preferred.

In the nonaqueous electrolytic solution of the present invention, acontent of the compound represented by the foregoing general formula(IV), which is contained in the nonaqueous electrolytic solution, ispreferably 0.001% to 5% by mass in the nonaqueous electrolytic solution.So long as the content is 5% by mass or less, there is less concern thata surface film is excessively formed on the electrode, thereby worseningthe low-temperature properties, and so long as the content is 0.001% bymass or more, the formation of a surface film is satisfactory, and theeffect for improving high-temperature storage properties is increased.Thus, the foregoing range is preferred. The content is more preferably0.05% by mass or more, and still more preferably 0.1% by mass or more inthe nonaqueous electrolytic solution. Its upper limit is more preferably3% by mass or less, and still more preferably 1% by mass or less.However, in the general formula (IV), in the case of a compound in whichX has an SiR⁴⁴R⁴⁵ group, its upper limit is preferably 3% or less, andmore preferably 2% or less.

In the nonaqueous electrolytic solution of the present invention, theuse of a combination of at least two or more selected from the SO₄group-containing compounds represented by any one of the foregoinggeneral formulae (I) to (IV) is more preferred because the effect forimproving electrochemical characteristics in a broad temperature rangeis increased, and a combination of at least one selected from the SO₄group-containing compounds represented by the foregoing general formula(I) and at least one selected from the SO₄ group-containing compoundsrepresented by any one of the foregoing general formulae (II) to (IV) isstill more preferred.

In the nonaqueous electrolytic solution of the present invention, bycombining at least one selected from the SO₄ group-containing compoundsrepresented by any one of the foregoing general formulae (I) to (IV)with a nonaqueous solvent, an electrolyte salt, and other additive asdescribed below, there is revealed a peculiar effect such that theelectrochemical characteristics are synergistically improved in a broadtemperature range.

[Nonaqueous Solvent]

Suitable examples of the nonaqueous solvent which is used for thenonaqueous electrolytic solution of the present invention include one ormore selected from a cyclic carbonate, a linear ester, a lactone, anether, and an amide. From the viewpoint of synergistically improving theelectrochemical characteristics in a broad temperature range, it ispreferred to contain a linear ester, it is more preferred to contain alinear carbonate, and it is the most preferred to contain both a cycliccarbonate and a linear carbonate.

The term “linear ester” is used as a concept including a linearcarbonate and a linear carboxylic acid ester.

Examples of the cyclic carbonate include one or more selected fromethylene carbonate (EC), propylene carbonate (PC), 1,2-butylenecarbonate, 2,3-butylene carbonate; a cyclic carbonate having acarbon-carbon unsaturated bond, such as vinylene carbonate (VC), vinylethylene carbonate (VEC), 4-ethynyl-1,3-dioxolan-2-one (EEC), etc.; anda cyclic carbonate having a fluorine atom, such as4-fluoro-1,3-dioxolan-2-one (FEC), trans- orcis-4,5-difluoro-1,3-dioxolan-2-one (the both will be hereunder namedgenerically as “DFEC”), etc. One or more selected from ethylenecarbonate, propylene carbonate, 4-fluoro-1,3-dioxolan-2-one, vinylenecarbonate, and 4-ethynyl-1,3-dioxolan-2-one (EEC) are more suitable.

Use of at least one of the aforementioned cyclic carbonates having acarbon-carbon unsaturated bond, such as a carbon-carbon double bond, acarbon-carbon triple bond, etc., or a fluorine atom is preferred becausea low-temperature load characteristic after high-temperature chargingstorage is much more improved, and it is more preferred to contain boththe aforementioned cyclic carbonate containing a carbon-carbonunsaturated bond and the aforementioned cyclic carbonate having afluorine atom. As the cyclic carbonate having a carbon-carbonunsaturated bond, VC, VEC, and EEC are more preferred, and as the cycliccarbonate having a fluorine atom, FEC and DFEC are more preferred.

A content of the cyclic carbonate having a carbon-carbon unsaturatedbond is preferably 0.07% by volume or more, more preferably 0.2% byvolume or more, and still more preferably 0.7% by volume or morerelative to a total volume of the nonaqueous solvent, and when an upperlimit thereof is preferably 7% by volume or less, more preferably 4% byvolume or less, and still more preferably 2.5% by volume or less,stability of a surface film at the time of high-temperature storage maybe much more increased without impairing Li ion permeability at lowtemperatures, and hence, such is preferred.

A content of the cyclic carbonate having a fluorine atom is preferably0.07% by volume or more, more preferably 4% by volume or more, and stillmore preferably 7% by volume or more relative to a total volume of thenonaqueous solvent, and when an upper limit thereof is preferably 35% byvolume or less, more preferably 25% by volume or less, and still morepreferably 15% by volume or less, stability of a surface film at thetime of high-temperature storage may be much more increased withoutimpairing Li ion permeability at low temperatures, and hence, such ispreferred.

In the case where the nonaqueous solvent contains both theaforementioned cyclic carbonate having a carbon-carbon unsaturated bondand the aforementioned cyclic carbonate having a fluorine atom, acontent of the cyclic carbonate having a carbon-carbon unsaturated bondis preferably 0.2% by volume or more, more preferably 3% by volume ormore, and still more preferably 7% by volume or more relative to acontent of the cyclic carbonate having a fluorine atom, and when anupper limit thereof is preferably 40% by volume or less, more preferably30% by volume or less, and still more preferably 15% by volume or less,stability of a surface film at the time of high-temperature storage maybe much more increased without impairing Li ion permeability at lowtemperatures, and hence, such is especially preferred.

When the nonaqueous solvent contains ethylene carbonate and/or propylenecarbonate, resistance of a surface film formed on an electrode becomessmall, and hence, such is preferred. A content of ethylene carbonateand/or propylene carbonate is preferably 3% by volume or more, morepreferably 5% by volume or more, and still more preferably 7% by volumeor more relative to a total volume of the nonaqueous solvent, and anupper limit thereof is preferably 45% by volume or less, more preferably35% by volume or less, and still more preferably 25% by volume or less.

These solvents may be used solely, and in the case where a combinationof two or more of the solvents is used, the electrochemicalcharacteristics are more improved in a broad temperature range, andhence, such is preferred, and use of a combination of three or morethereof is especially preferred. As suitable combinations of thesecyclic carbonates, EC and PC; EC and VC; PC and VC; VC and FEC; EC andFEC; PC and FEC; FEC and DFEC; EC and DFEC; PC and DFEC; VC and DFEC;VEC and DFEC; VC and EEC; EC and EEC; EC, PC and VC; EC, PC and FEC; EC,VC and FEC; EC, VC and VEC; EC, VC and EEC; EC, EEC and FEC; PC, VC andFEC; EC, VC and DFEC; PC, VC and DFEC; EC, PC, VC and FEC; EC, PC, VCand DFEC; and the like are preferred. Among the aforementionedcombinations, combinations, such as EC and VC; EC and FEC; PC and FEC;EC, PC and VC; EC, PC and FEC; EC, VC and FEC; EC, VC and EEC; EC, EECand FEC; PC, VC and FEC; EC, PC, VC and FEC; etc., are more preferred.

As the linear ester, there are suitably exemplified one or moreasymmetric linear carbonates selected from methyl ethyl carbonate (MEC),methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methylbutyl carbonate, and ethyl propyl carbonate; one or more symmetriclinear carbonates selected from dimethyl carbonate (DMC), diethylcarbonate (DEC), dipropyl carbonate, and dibutyl carbonate; and one ormore linear carboxylic acid esters selected from pivalic acid esters,such as methyl pivalate, ethyl pivalate, propyl pivalate, etc., methylpropionate, ethyl propionate, methyl acetate, and ethyl acetate.

Among the aforementioned linear esters, linear esters having a methylgroup, which are selected from dimethyl carbonate, methyl ethylcarbonate, methyl propyl carbonate, methyl isopropyl carbonate, methylbutyl carbonate, methyl propionate, methyl acetate, and ethyl acetate,are preferred, and linear carbonates having a methyl group areespecially preferred.

In the case of using a linear carbonate, it is preferred to use two ormore kinds thereof. Furthermore, it is more preferred that both asymmetric linear carbonate and an asymmetric linear carbonate arecontained, and it is still more preferred that a content of thesymmetric linear carbonate is more than that of the asymmetric linearcarbonate.

Although a content of the linear ester is not particularly limited, itis preferred to use the linear ester in an amount in the range of from60 to 90% by volume relative to a total volume of the nonaqueoussolvent. When the content is 60% by volume or more, the viscosity of thenonaqueous electrolytic solution does not become excessively high,whereas it is 90% by volume or less, there is less concern that anelectroconductivity of the nonaqueous electrolytic solution decreases,thereby worsening the electrochemical characteristics in a broadtemperature range, and therefore, it is preferred that the content ofthe linear ester falls within the foregoing range.

A proportion of the volume of the symmetric linear carbonate occupyingin the linear carbonate is preferably 51% by volume or more, and morepreferably 55% by volume or more. An upper limit thereof is morepreferably 95% by volume or less, and still more preferably 85% byvolume or less. It is especially preferred that dimethyl carbonate iscontained as the symmetric linear carbonate. It is more preferred thatthe asymmetric linear carbonate has a methyl group, and methyl ethylcarbonate is especially preferred.

The aforementioned case is preferred because the electrochemicalcharacteristics in a much broader temperature range are improved.

As for a proportion of the cyclic carbonate and the linear carbonate,from the viewpoint of improving the electrochemical characteristics in abroad temperature range, a ratio of the cyclic carbonate to the linearcarbonate (volume ratio) is preferably from 10/90 to 45/55, morepreferably from 15/85 to 40/60, and especially preferably from 20/80 to35/65.

As other nonaqueous solvents, there are suitably exemplified one or moreselected from cyclic ethers, such as tetrahydrofuran,2-methyltetrahydrofuran, 1,4-dioxane, etc.; linear ethers, such as1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane, etc.;amides, such as dimethylformamide, etc.; sulfones, such as sulfolane,etc.; and lactones, such as γ-butyrolactone, γ-valerolactone,α-angelicalactone, etc.

As for the aforementioned nonaqueous solvent, in order to achieveappropriate physical properties, a mixture thereof is generally used. Asa combination thereof, for example, there are suitably exemplified acombination of a cyclic carbonate and a linear carbonate, a combinationof a cyclic carbonate and a linear carboxylic acid ester, a combinationof a cyclic carbonate, a linear carbonate, and a lactone, a combinationof a cyclic carbonate, a linear carbonate, and an ether, a combinationof a cyclic carbonate, a linear carbonate, and a linear carboxylic acidester, and the like.

For the purpose of improving the electrochemical characteristics in amuch broader temperature range, it is preferred to further add otheradditive in the nonaqueous electrolytic solution.

As specific examples of other additive, there are suitably exemplifiedthe following compounds (a) to (j).

(a) Nitrile

One or more nitriles selected from acetonitrile, propionitrile,succinonitrile, glutaronitrile, adiponitrile, pimelonitrile,suberonitrile, and sebaconitrile.

Above, one or more selected from succinonitrile, glutaronitrile,adiponitrile, and pimelonitrile are more preferred.

(b) Aromatic Compound:

Aromatic compounds having a branched alkyl group, such ascyclohexylbenzene, fluorocyclohexylbenzene compounds (e.g.,1-fluoro-2-cyclohexylbenzene, 1-fluoro-3-cyclohexylbenzene, or1-fluoro-4-cyclohexylbenzene), tert-butylbenzene, tert-amylbenzene,1-fluoro-4-tert-butylbenzene, etc.; and aromatic compounds, such asbiphenyl, terphenyl (o-, m-, or p-form), diphenyl ether, fluorobenzene,difluorobenzene (o-, m-, or p-form), anisole, 2,4-difluoroanisole,partial hydrides of terphenyl (e.g., 1,2-dicyclohexylbenzene,2-phenylbicyclohexyl, 1,2-diphenylcyclohexane, or o-cyclohexylbiphenyl),etc.

Above all, one or more selected from biphenyl, terphenyl (o-, m-, orp-form), fluorobenzene, cyclohexylbenzene, tert-butylbenzene, andtert-amylbenzene are more preferred, and one or more selected frombiphenyl, o-terphenyl, fluorobenzene, cyclohexylbenzene, andtert-amylbenzene are especially preferred.

(c) Isocyanate Compound:

One or more isocyanate compounds selected from methyl isocyanate, ethylisocyanate, butyl isocyanate, phenyl isocyanate, tetramethylenediisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate,1,4-phenylene diisocyanate, 2-isocyanatoethyl acrylate, and2-isocyanatoethyl methacrylate.

Above all, one or more selected from hexamethylene diisocyanate,octamethylene diisocyanate, 2-isocyanatoethyl acrylate, and2-isocyanatoethyl methacrylate are more preferred.

(d) Triple Bond-Containing Compound:

One or more triple bond-containing compounds selected from 2-propynylmethyl carbonate, 2-propynyl acetate, 2-propynyl formate, 2-propynylmethacrylate, 2-propynyl methanesulfonate, 2-propynyl vinylsulfonate,2-propynyl 2-(methanesulfonyloxy)propionate, di(2-propynyl) oxalate,methyl 2-propynyl oxalate, ethyl 2-propynyl oxalate, di(2-propynyl)glutarate, 2-butyne-1,4-diyl dimethanesulfonate, 2-butyne-1,4-diyldiformate, and 2,4-hexadiyne-1,6-diyl dimethanesulfonate.

Above all, one or more selected from 2-propynyl methyl carbonate,2-propynyl methacrylate, 2-propynyl methanesulfonate, 2-propynylvinylsulfonate, 2-propynyl 2-(methanesulfonyloxy)propionate,di(2-propynyl) oxalate, methyl 2-propynyl oxalate, ethyl 2-propynyloxalate, and 2-butyne-1,4-diyl dimethanesulfonate are preferred, and oneor more selected from 2-propynyl methanesulfonate, 2-propynylvinylsulfonate, 2-propynyl 2-(methanesulfonyloxy)propionate,di(2-propynyl) oxalate, and 2-butyne-1,4-diyl dimethanesulfonate aremore preferred.

(e) S═O Group-Containing Compound:

One or more S═O group-containing compounds selected from sultones, suchas 1,3-propanesultone, 1,3-butanesultone, 2,4-butanesultone,1,4-butanesultone, 1,3-propenesultone, 2,2-dioxide-1,2-oxathiolane-4-ylacetate, 5,5-dimethyl-1,2-oxathiolane-4-one 2,2-dioxide, etc.; cyclicsulfite, such as ethylene sulfite, hexahydrobenzo[1,3,2]dioxathiolane-2-oxide (also called 1,2-cyclohexanediol cyclic sulfite),5-vinyl-hexahydro-1,3,2-benzodioxathiol-2-oxide, etc.; sulfonic acidester compounds, such as butane-2,3-diyl dimethanesulfonate,butane-1,4-diyl dimethanesulfonate, methylene methanedisulfonate, etc.;and vinylsulfone compounds, such as divinylsulfone,1,2-bis(vinylsulfonyl)ethane, bis(2-vinylsulfonylethyl) ether, etc.

Above all, it is preferred to use a cyclic or linear S═Ogroup-containing compound selected from sultones, cyclic sulfites,sulfonic acid esters, and vinylsulfones (however, the triplebond-containing compounds and the specified lithium salts represented bythe foregoing general formula (I) are not included).

Suitable examples of the cyclic S═O group-containing compound includeone or more selected from 1,3-propanesultone, 1,3-butanesultone,1,4-butanesultone, 2,4-butanesultone, 1,3-propenesultone,2,2-dioxide-1,2-oxathiolane-4-yl acetate,5,5-dimethyl-1,2-oxathiolane-4-one, 2,2-dioxide, methylenemethanedisulfonate, ethylene sulfite, and4-(methylsulfonylmethyl)-1,3,2-dioxathiolane 2-oxide.

Suitable examples of the linear S═O group-containing compound includeone or more selected from butane-2,3-diyl dimethanesulfonate,butane-1,4-diyl dimethanesulfonate, dimethyl methanedisulfonate,pentafluorophenyl methanesulfonate, divinylsulfone, andbis(2-vinylsulfonylethyl) ether.

Among the aforementioned cyclic or linear S═O group-containingcompounds, one or more selected from 1,3-propanesultone,1,4-butanesultone, 2,4-butanesultone, 2,2-dioxide-1,2-oxathiolane-4-ylacetate, 5,5-dimethyl-1,2-oxathiolane-4-one 2,2-dioxide, butane-2,3-diyldimethanesulfonate, pentafluorophenyl methanesulfonate, anddivinylsulfone.

(f) Cyclic Acetal Compound:

Cyclic acetal compounds, such as 1,3-dioxolane, 1,3-dioxane,1,3,5-trioxane, etc. Above all, 1,3-dioxolane and 1,3-dioxane arepreferred, and 1,3-dioxane is more preferred.

(g) Phosphorus-Containing Compound:

Examples thereof include one or more phosphorus-containing compoundsselected from trimethyl phosphate, tributyl phosphate, trioctylphosphate, tris(2,2,2-trifluoroethyl)phosphate,bis(2,2,2-trifluoroethyl)methyl phosphate, bis(2,2,2-trifluoroethy)ethylphosphate, bis(2,2,2-trifluoroethyl)2,2-difluroethyl phosphate,bis(2,2,2-trifluoroethyl)2,2,3,3-tetrafluoropropyl phosphate,bis(2,2-difluoroethyl)2,2,2-trifluoroethyl phosphate,bis(2,2,3,3-tetrafluoropropyl)2,2,2-trifluoroethyl phosphate,(2,2,2-trifluroethyl)(2,2,3,3-tetrafluoropropyl)methyl phosphate,tris(1,1,1,3,3,3-hexafluoropropan-2-yl)phosphate, methylmethylenebisphosphonate, ethyl methylenebisphosphonate, methylethylenebisphosphonate, ethyl ethylenebisphosphonate, methylbutylenebisphosphonate, ethyl butylenebisphosphonate, methyl2-(dimethylphosphoryl)acetate, ethyl 2-(dimethylphosphoryl)acetate,methyl 2-(diethylphosphoryl)acetate, ethyl 2-(diethylphosphoryl)acetate,2-propynyl 2-(dimethylphosphoryl)acetate, 2-propynyl2-(diethylphosphoryl)acetate, methyl 2-(dimethoxyphosphoryl)acetate,ethyl 2-(dimethoxyphosphoryl)acetate, methyl2-(diethoxyphosphoryl)acetate, ethyl 2-(diethoxyphosphoryl)acetate,2-propynyl 2-(dimethoxyphosphoryl)acetate, 2-propynyl2-(diethoxyphosphoryl)acetate, methyl pyrophosphate, and ethylpyrophosphate.

Above all, tris(2,2,2-trifluoroethyl)phosphate,tris(1,1,1,3,3,3-hexafluoropropan-2-yl)phosphate, methyl2-(dimethylphosphoryl)acetate, ethyl 2-(dimethylphosphoryl)acetate,methyl 2-(diethylphosphoryl)acetate, ethyl 2-(diethylphosphoryl)acetate,2-propynyl 2-(dimethylphosphoryl)acetate, 2-propynyl2-(diethylphosphoryl)acetate, methyl 2-(dimethoxyphosphoryl)acetate,ethyl 2-(dimethoxyphosphoryl)acetate, methyl2-(diethoxyphosphoryl)acetate, ethyl 2-(diethoxyphosphoryl)acetate,2-propynyl 2-(dimethoxyphosphoryl)acetate, and 2-propynyl2-(diethoxyphosphoryl)acetate are preferred, andtris(2,2,2-trifluoroethyl)phosphate,tris(1,1,1,3,3,3-hexafluoropropan-2-yl)phosphate, ethyl2-(diethylphosphoryl)acetate, 2-propynyl 2-(dimethylphosphoryl)acetate,2-propynyl 2-(diethylphosphoryl)acetate, ethyl2-(diethoxyphosphoryl)acetate, 2-propynyl2-(dimethoxyphosphoryl)acetate, and 2-propynyl2-(diethoxyphosphoryl)acetate are more preferred.

(h) Cyclic Acid Anhydride:

Suitable examples thereof include linear carboxylic anhydrides, such asacetic anhydride, propionic anhydride, etc., and cyclic acid anhydrides,such as succinic anhydride, maleic anhydride, 2-allyl succinicanhydride, glutaric anhydride, itaconic anhydride, 3-sulfo-propionicanhydride, etc.

Above all, succinic anhydride, maleic anhydride, and 2-allyl succinicanhydride are preferred, and succinic anhydride and 2-allyl succinicanhydride are more preferred.

(i) Cyclic Phosphazene Compound:

Suitable examples thereof include cyclic phosphazene compounds, such asmethoxypentafluorocyclotriphosphazene,ethoxypentafluorocyclotriphosphazene,phenoxypentafluorocyclotriphosphazene,ethoxyheptafluorocyclotetraphosphazene, etc.

Above all, cyclic phosphazene compounds, such asmethoxypentafluorocyclotriphosphazene,ethoxypentafluorocyclotriphosphazene,phenoxypentafluorocyclotriphosphazene, etc., are preferred, andmethoxypentafluorocyclotriphosphazene, andethoxypentafluorocyclotriphosphazene are more preferred.

(j) Fluorine-Containing Compound:

Examples of the fluorine-containing compound include a compoundrepresented by the following general formula (V):

wherein each of R⁵¹ to R⁵³ independently represents an alkyl grouphaving 1 to 12 carbon atoms, an alkenyl group having 2 to 3 carbonatoms, an aryl group having 6 to 8 carbon atoms, or an S(═O)₂F group.

Each of R⁵¹ to R⁵³ is preferably an alkyl group having 1 to 4 carbonatoms, an alkenyl group having 2 carbon atoms, or an aryl group having 6to 7 carbon atoms, more preferably an alkyl group having 1 to 2 carbonatoms or an aryl group having 6 carbon atoms, and still more preferablyan alkyl group having 1 carbon atom.

R⁵¹ to R⁵³ may be bonded to each other to form a ring.

As specific examples of R⁵¹ to R⁵³, there are suitably exemplified astraight-chain alkyl group, such as a methyl group, an ethyl group, ann-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group,an n-heptyl group, an n-octyl group, an n-decyl group, an n-dodecylgroup, etc.; a branched alkyl group, such as an isopropyl group, asec-butyl group, a tert-butyl group, a tert-amyl group, a 2-ethylhexylgroup, etc.; a cycloalkyl group, such as a cyclopentyl group, acyclohexyl group, etc.; an alkenyl group, such as a vinyl group, a2-propenyl group, etc.; an aryl group, such as a phenyl group, a2-methylphenyl group, a 3-methylphenyl group, a 4-methylphenyl group, a4-tert-butylphenyl group, a 2-fluorophenyl group, a 4-fluorophenylgroup, a 4-trifluoromethylphenyl group, a 2,4-difluorophenyl group, aperfluorophenyl group, etc.; and an S(═O)₂F group.

Above all, a methyl group, an ethyl group, an n-propyl group, an n-butylgroup, an isopropyl group, a sec-butyl group, a tert-butyl group, avinyl group, a phenyl group, a 4-methylphenyl group, a 4-fluorophenylgroup, and a perfluorophenyl group are more preferred, and a methylgroup is still more preferred.

As the fluorine-containing compound represented by the foregoing generalformula (V), in addition to bis(fluorosulfonyloxy)dimethylsilane,specifically, there are suitably exemplified the following compounds.

Among the aforementioned compounds, trimethylsilyl fluorosulfonate(Compound A41), triethylsilyl fluorosulfonate (Compound A42),triisopropylsilyl fluorosulfonate (Compound A43),tert-butyldimethylsilyl fluorosulfonate (Compound A44), andtert-butyldiphenylsilyl fluorosulfonate (Compound A47) are preferred,trimethylsilyl fluorosulfonate (Compound A41), triethylsilylfluorosulfonate (Compound A42), and triisopropylsilyl fluorosulfonate(Compound A43) are more preferred, and trimethylsilyl fluorosulfonate(Compound A41) is still more preferred.

Among the foregoing, when at least one selected from the nitrile (a),the aromatic compound (b), and the isocyanate compound (c) is contained,the electrochemical characteristics in a much broader temperature rangeare improved, and hence, such is preferred.

A content of each of the compounds (a) to (c) is preferably 0.01 to 7%by mass in the nonaqueous electrolytic solution. In this range, asurface film is thoroughly formed without becoming excessively thick,and the effect for improving electrochemical characteristics in a broadtemperature range is increased. The content is more preferably 0.05% bymass or more, and still more preferably 0.1% by mass or more in thenonaqueous electrolytic solution. Its upper limit is more preferably 5%by mass or less, and still more preferably 3% by mass or less.

When the triple bond-containing compound (d), the cyclic or linear S═Ogroup-containing compound (e) selected from a sultone compound, a cyclicsulfite, a sulfonic acid ester, and a vinylsulfone, the cyclic acetalcompound (f), the phosphorus-containing compound (g), the cyclic acidanhydride (h), the cyclic phosphazene compound (i), or thefluorine-containing compound (j) is contained, the electrochemicalcharacteristics in a much broader temperature range are improved, andhence, such is preferred.

A content of each of the compounds (d) to (j) is preferably 0.001 to 5%by mass in the nonaqueous electrolytic solution. In this range, asurface film is thoroughly formed without becoming excessively thick,and the effect for improving electrochemical characteristics in a broadtemperature range is increased. The content is more preferably 0.01% bymass or more, and still more preferably 0.1% by mass or more in thenonaqueous electrolytic solution. Its upper limit is more preferably 3%by mass or less, and still more preferably 2% by mass or less.

[Electrolyte Salt]

As the electrolyte salt which is used in the present invention, thereare suitably exemplified the following lithium salts.

[Li salt—Class 1]

One or more “complex salts of a Lewis acid and LiF” selected from LiPF₆,LiBF₄, LiAsF₆, LiSbF₆, LiPF₄(CF₃)₂, LiPF₃(C₂F₅)₃, LiPF₃(CF₃)₃,LiPF₃(iso-C₃FO₃, and LiPF₅(iso-C₃F₇) are suitably exemplified. Aboveall, LiPF₆, LiBF₄, and LiAsF₆ are preferred, and LiPF₆ and LiBF₄ aremore preferred.

[Li Salt—Class 2]

One or more “imide or methide lithium salts” selected from LiN(SO₂O₂,LiN(SO₂CFO₂, LiN(SO₂C₂F₅)₂, (CF₂)₂(SO₂)₂NLi (cyclic), (CF₂)₃(SO₂)₂NLi(cyclic), and LiC(SO₂CFO₃ are suitably exemplified. Above all,LiN(SO₂O₂, LiN(SO₂CF₃)₂, and LiN(SO₂C₂F₅)₂ are preferred, and LiN(SO₂O₂and LiN(SO₂CFO₂ are more preferred.

[Li salt—Class 3]

One or more “S(═O)₂O structure-containing lithium salts” selected fromLiSO₃F, LiCF₃SO₃, CH₃SO₄Li, C₂H₅SO₄Li, C₃H₇SO₄Li, lithiumtrifluoro((methanesulfonyl)oxy)borate (LiTFMSB), and lithiumpentafluoro((methanesulfonyl)oxy)phosphate (LiPFMSP) are suitablyexemplified. Above all, LiSO₃F, CH₃SO₄Li, C₂H₅SO₄Li, and LiTFMSB aremore preferred.

[Li salt—Class 4]

One or more “P═O or Cl═O structure-containing lithium salts” selectedfrom LiPO₂F₂, Li₂PO₃F, and LiClO₄ are suitably exemplified. Above all,LiPO₂F₂ and Li₂PO₃F are preferred.

[Li salt—Class 5]

One or more “lithium salts containing an oxalate complex as an anion”selected from lithium bis[oxalate-O,O′]borate (LiBOB), lithium difluoro[oxalate-O,O′]borate, lithium difluorobis[oxalate-O,O′]phosphate(LiPFO), and lithium tetrafluoro[oxalate-O,O′]phosphate are suitablyexemplified. Above all, LiBOB and LiPFO are more preferred.

These compounds may be used solely or in admixture of two or more kindsthereof.

Of those, one or more selected from LiPF₆, LiPO₂F₂, Li₂PO₃F, LiBF₄,LiSO₃F, lithium trifluoro((methanesulfonyl)oxy)borate (LiTFMSB),LiN(SO₂F)₂, LiN(SO₂CF₃)₂, LiN(SO₂C₂F₅)₂, lithium bis[oxalate-O,O′]borate(LiBOB), lithium difluorobis[oxalate-O,O′]phosphate (LiPFO), and lithiumtetrafluoro[oxalate-O,O′]phosphate are preferred, one or more selectedfrom LiPF₆, LiBF₄, LiSO₃F, lithium trifluoro((methanesulfonyl)oxy)borate(LiTFMSB), LiPO₂F₂, LiN(SO₂CF₃)₂, LiN(SO₂F)₂, lithiumbis[oxalate-O,O′]borate (LiBOB), and lithiumdifluorobis[oxalate-O,O′]phosphate (LiPFO) are more preferred, and LiPF₆is most preferably used.

In general, a concentration of the lithium salt is preferably 0.3 M ormore, more preferably 0.7 M or more, and still more preferably 1.1 M ormore relative to the nonaqueous solvent. Its upper limit is preferably2.5 M or less, more preferably 2.0 M or less, and still more preferably1.6 M or less.

As a suitable combination of these lithium salts (excluding at least oneselected from the SO₄ group-containing compounds represented by any oneof the foregoing general formulae (I) to (IV)), a combination includingLiPF₆ and one or more selected from LiSO₃F, LiPO₂F₂, LiN(SO₂F)₂,LiN(SO₂CF₃)₂, lithium bis[oxalate-O,O′]borate (LiBOB), and lithiumdifluorobis[oxalate-O,O′]phosphate (LiPFO) is more preferred. When aproportion of the lithium salt other than LiPF₆ occupying in thenonaqueous solvent is 0.001 M or more, the effect for improvingelectrochemical characteristics at high temperatures is liable to beexhibited, whereas when it is 0.8 M or less, there is less concern thatthe effect for improving electrochemical characteristics at hightemperature is worsened, and hence, such is preferred. The proportion ofthe lithium salt other than LiPF₆ is preferably 0.01 M or more,especially preferably 0.03 M or more, and most preferably 0.04 M ormore. Its upper limit is preferably 0.6 M or less, more preferably 0.4 Mor less, and especially preferably 0.2 M or less.

In the case where LiPF₆ is contained in the nonaqueous electrolyticsolution, when a ratio of at least one selected from the SO₄group-containing compounds represented by any one of the foregoinggeneral formulae (I) to (IV) of the invention of the present applicationto LiPF₆ in terms of a molar concentration is 0.0005 or more, the effectfor improving electrochemical characteristics at high temperatures isliable to be exhibited, whereas when it is 0.3 or less, there is lessconcern that the effect for improving electrochemical characteristics athigh temperatures is worsened, and hence, such is preferred. Its lowerlimit is more preferably 0.001 or more, and still more preferably 0.005or more. Its upper limit is more preferably 0.2 or less, and still morepreferably 0.1 or less.

As for the lithium salt which is combined with the SO₄ group-containingcompound represented by the foregoing general formula (I-3), when acombination of lithium salts of plural groups among the Li salt—Classes1 to 5 is used, the effect for improving electrochemical characteristicsin a broad temperature range is increased, and hence, such is morepreferred. A combination of the Class 1 with at least one of the Classes2 to 5 is still more preferred. Above all, a combination of the Class 1with at least one of the Classes 3 to 5 is especially preferred.

In the case where the Class 1 is combined with at least one of theClasses 2 to 5, a proportion of a total mass of the lithium salts of theClasses 2 to 5 relative to a total mass of the lithium salts of theClasses 1 to 5 is preferably 0.1% or more, and more preferably 1% ormore. Its upper limit is preferably 49% or less, and more preferably 45%or less.

A lower limit of a proportion of the SO₄ group-containing compoundrepresented by the general formula (I-3) in the whole of the electrolytesalts is preferably 25% or more, and more preferably 30% or morerelative to a total mass of the whole of the electrolyte salts. An upperlimit of the proportion is 100%, more preferably 80% or less, andespecially preferably 60% or less.

In general, a molar concentration of the whole of the electrolyte saltscontained in the nonaqueous electrolytic solution containing the SO₄group-containing compound represented by the general formula (I-3) ispreferably 0.3 M or more, more preferably 0.7 M or more, and still morepreferably 1.1 M or more relative to the nonaqueous solvent. Its upperlimit is preferably 2.5 M or less, more preferably 2.0 M or less, andstill more preferably 1.6 M or less.

In general, a concentration of the whole of the electrolyte saltscontained in the nonaqueous electrolytic solution containing the SO₄group-containing compound represented by the general formula (I-3) ispreferably 4% by mass or more, more preferably 9% by mass or more, andstill more preferably 13% by mass or more. Its upper limit is preferably30% by mass or less, more preferably 25% by mass or less, and still morepreferably 20% by mass or less.

[Production of Nonaqueous Electrolytic Solution]

The nonaqueous electrolytic solution of the present invention may be,for example, obtained by mixing the aforementioned nonaqueous solventand adding at least one selected from the SO₄ group-containing compoundsrepresented by any one of the foregoing general formulae (I) to (IV) tothe aforementioned electrolyte salt and the nonaqueous electrolyticsolution.

At this time, the nonaqueous solvent used and the compounds added to thenonaqueous electrolytic solution are preferably purified previously toreduce as much as possible the content of impurities, in such an extentthat does not extremely deteriorate the productivity.

The nonaqueous electrolytic solution of the present invention may beused in first to fourth energy storage devices shown below, in which thenonaqueous electrolyte may be used not only in the form of a liquid butalso in the form of gel. Furthermore, the nonaqueous electrolyticsolution of the present invention may also be used for a solid polymerelectrolyte. Among those, the nonaqueous electrolytic solution ispreferably used in the first energy storage device using a lithium saltas the electrolyte salt (i.e., for a lithium battery) or in the fourthenergy storage device (i.e., for a lithium ion capacitor), morepreferably used in a lithium battery, and still more preferably used ina lithium secondary battery.

[First Energy Storage Device (Lithium Battery)]

The lithium battery as referred to in the present specification is ageneric name for a lithium primary battery and a lithium secondarybattery. In the present specification, the term, lithium secondarybattery, is used as a concept that includes a so-called lithium ionsecondary battery. The lithium battery of the present invention containsa positive electrode, a negative electrode, and the aforementionednonaqueous electrolytic solution having an electrolyte salt dissolved ina nonaqueous solvent. Other constitutional members used than thenonaqueous electrolytic solution, such as the positive electrode, thenegative electrode, etc., are not particularly limited.

For example, as the positive electrode active material for lithiumsecondary batteries, usable is a complex metal oxide containing lithiumand one or more selected from cobalt, manganese, and nickel. Thesepositive electrode active materials may be used solely or in combinationof two or more kinds thereof.

As the lithium complex metal oxides, for example, one or more selectedfrom LiCoO₂, LiMn₂O₄, LiNiO₂, LiCo_(1-x)Ni_(x)O₂ (0.01<x<1),LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂, LiNi_(1/2)Mn_(3/2)O₄, andLiCo_(0.98)Mg_(0.02)O₂ are exemplified. These materials may be used as acombination, such as a combination of LiCoO₂ and LiMn₂O₄, a combinationof LiCoO₂ and LiNiO₂, and a combination of LiMn₂O₄ and LiNiO₂.

For improving the safety on overcharging and the cycle properties, andfor enabling the use at a charge potential of 4.3 V or more, a part ofthe lithium complex metal oxide may be substituted with other elements.For example, a part of cobalt, manganese, or nickel may be substitutedwith at least one or more elements of Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga,Zn, Cu, Bi, Mo, La, etc.; or a part of O may be substituted with S or F;or the oxide may be coated with a compound containing any of such otherelements.

Of the aforementioned positive electrode active materials, preferred arelithium complex metal oxides, such as LiCoO₂, LiMn₂O₄, and LiNiO₂, withwhich the charge potential of the positive electrode in a fully-chargedstate may be used at 4.3 V or more based on Li; and more preferred arelithium complex metal oxides, such as LiCo_(1-x)M_(x)O₂ (wherein M isone or more elements selected from Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga,Zn, and Cu; and 0.001≦x≦0.05), LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂,LiNi_(1/2)Mn_(3/2)O₄, and a solid solution of Li₂MnO₃ and LiMO₂ (whereinM is a transition metal, such as Co, Ni, Mn, Fe, etc.), that may be usedat 4.4 V or more. The use of the lithium complex metal oxide capable ofacting at a high charge voltage may worsen the electrochemicalcharacteristics particularly on using in a broad temperature range dueto the reaction with the electrolytic solution on charging, but in thelithium secondary battery according to the present invention, theelectrochemical characteristics may be prevented from worsening.

In particular, in the case of a positive electrode containing Mn, thereis a tendency that the resistance of the battery is liable to increasewith elution of an Mn ion from the positive electrode, so that there isa tendency that when used in a broad temperature range, theelectrochemical characteristics are liable to be worsened. However, inthe lithium secondary battery according to the present invention, theworsening of these electrochemical characteristics may be suppressed,and hence, such is preferred.

Furthermore, a lithium-containing olivine-type phosphate may also beused as the positive electrode active material. Especially preferred arelithium-containing olivine-type phosphates containing one or moreselected from iron, cobalt, nickel, and manganese. Specific examplesthereof include one or more selected from LiFePO₄, LiCoPO₄, LiNiPO₄, andLiMnPO₄.

These lithium-containing olivine-type phosphates may be partlysubstituted with any other element; and for example, a part of iron,cobalt, nickel, or manganese therein may be substituted with one or moreelements selected from Co, Mn, Ni, Mg, Al, B, Ti, V, Nb, Cu, Zn, Mo, Ca,Sr, W, and Zr; or the phosphates may also be coated with a compoundcontaining any of these other elements or with a carbon material. Amongthose, LiFePO₄ or LiMnPO₄ is preferred.

The lithium-containing olivine-type phosphate may be used, for example,in combination with the aforementioned positive electrode activematerial.

For the positive electrode for lithium primary batteries, there aresuitably exemplified oxides or chalcogen compounds of one or more metalelements, such as CuO, Cu₂O, Ag₂O, Ag₂CrO₄, CuS, Cu₅O₄, TiO₂, TiS₂,SiO₂, SnO, V₂O₅, V₆O₁₂, VO_(x), Nb₂O₅, Bi₂O₃, Bi₂Pb₂O₅, Sb₂O₃, CrO₃,Cr₂O₃, MoO₃, WO₃, SeO₂, MnO₂, Mn₂O₃, Fe₂O₃, FeO, Fe₃O₄, Ni₂₀₃, NiO,CoO₃, CoO, etc.; sulfur compounds, such as SO₂, SOCl₂, etc.; and carbonfluorides (graphite fluoride) represented by a general formula(CF_(x))_(n). Of those, MnO₂, V₂O₅, graphite fluoride, and the like arepreferred.

In the case where a pH of a supernatant at the time of dispersing 10 gof the aforementioned positive electrode active material in 100 mL ofdistilled water is 10.0 to 12.5, the effect for improvingelectrochemical characteristics in a much broader temperature range isliable to be obtained, and hence, such is preferred. The case where thepH is 10.5 to 12.0 is more preferred.

In the case where Ni is contained as the element in the positiveelectrode, since there is a tendency that impurities, such as LiOH,etc., in the positive electrode active material increase, the effect forimproving electrochemical characteristics in a much broader temperaturerange is liable to be obtained, and hence, such is preferred. The casewhere an atomic concentration of Ni in the positive electrode materialis 5 to 25 atomic % is more preferred, and the case where it is 8 to 21atomic % is especially preferred.

An electroconductive agent of the positive electrode is not particularlylimited so long as it is an electron-conductive material that does notundergo a chemical change. Examples thereof include graphites, such asnatural graphite (e.g., flaky graphite, etc.), artificial graphite,etc.; one or more carbon blacks selected from acetylene black, Ketjenblack, channel black, furnace black, lamp black, and thermal black; andthe like. Graphite and carbon black may be properly mixed and used. Anaddition amount of the electroconductive agent to the positive electrodemixture is preferably from 1 to 10% by mass, and especially preferablyfrom 2 to 5% by mass.

The positive electrode may be produced by mixing the aforementionedpositive electrode active material with an electroconductive agent, suchas acetylene black, carbon black, etc., and a binder, such aspolytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), acopolymer of styrene and butadiene (SBR), a copolymer of acrylonitrileand butadiene (NBR), carboxymethyl cellulose (CMC), anethylene-propylene-diene terpolymer, etc., adding a high-boiling pointsolvent, such as 1-methyl-2-pyrrolidone, etc., thereto, followed bykneading to prepare a positive electrode mixture, applying this positiveelectrode mixture onto a collector, such as an aluminum foil, astainless steel-made lath plate, etc., and drying and shaping theresultant under pressure, followed by a heat treatment in vacuum at atemperature of from about 50° C. to 250° C. for about 2 hours.

A density of a portion of the positive electrode except for thecollector is generally 1.5 g/cm³ or more, and for the purpose of furtherincreasing the capacity of the battery, the density is preferably 2g/cm³ or more, more preferably 3 g/cm³ or more, and still morepreferably 3.6 g/cm³ or more. An upper limit thereof is preferably 4g/cm³ or less.

As the negative electrode active material for lithium secondarybatteries, one or more selected from a lithium metal, lithium alloys, orcarbon materials capable of absorbing and releasing lithium [e.g.,graphitizable carbon, non-graphitizable carbon having a spacing of the(002) plane of 0.37 nm or more, graphite having a spacing of the (002)plane of 0.34 nm or less, etc.], tin (elemental substance), tincompounds, silicon (elemental substance), silicon compounds, lithiumtitanate compounds, such as Li₄Ti₅O₁₂, etc., or the like may be used incombination.

Of those, in absorbing and releasing ability of a lithium ion, it ismore preferred to use a high-crystalline carbon material, such asartificial graphite, natural graphite, etc.; and it is still morepreferred to use a carbon material having a graphite-type crystalstructure in which a lattice (002) spacing (d₀₀₂) is 0.340 nm(nanometers) or less, especially from 0.335 to 0.337 nm.

In particular, it is preferred to use an artificial graphite particlehaving a bulky structure in which plural flat graphite fine particlesare mutually gathered or bound in non-parallel, or a graphite particleprepared by subjecting a flaky natural graphite particle to aspheroidizing treatment by repeatedly giving a mechanical action, suchas compression force, frictional force, shear force, etc.

When a ratio [I(110)/I(004)] of a peak intensity I(110) of the (110)plane to a peak intensity I(004) of the (004) plane of the graphitecrystal, which is obtained from the X-ray diffraction measurement of anegative electrode sheet at the time of shaping under pressure of aportion of the negative electrode except for the collector in a densityof 1.5 g/cm³ or more, is 0.01 or more, the electrochemicalcharacteristics in a much broader temperature range are improved, andhence, such is preferred. The peak intensity ratio [I(110)/I(004)] ismore preferably 0.05 or more, and still more preferably 0.1 or more.When excessively treated, there may be the case where the crystallinityis worsened, and the discharge capacity of the battery is worsened, andtherefore, an upper limit of the peak intensity ratio [I(110)/I(004)] ispreferably 0.5 or less, and more preferably 0.3 or less.

When the high-crystalline carbon material (core material) is coated witha carbon material that is more low-crystalline than the core material,the electrochemical characteristics in a broad temperature range becomemuch more favorable, and hence, such is preferred. The crystallinity ofthe carbon material of the coating may be confirmed by TEM.

When the high-crystalline carbon material is used, there is a tendencythat it reacts with the nonaqueous electrolytic solution on charging,thereby worsening the electrochemical characteristics at lowtemperatures or high temperatures due to an increase of the interfacialresistance; however, in the lithium secondary battery according to thepresent invention, the electrochemical characteristics in a broadtemperature range become favorable.

As the metal compound capable of absorbing and releasing lithium,serving as a negative electrode active material, there are exemplifiedcompounds containing at least one metal element, such as Si, Ge, Sn, Pb,P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ag, Mg, Sr, Ba, etc.These metal compounds may be in any form including an elementalsubstance, an alloy, an oxide, a nitride, a sulfide, a boride, and analloy with lithium, and any of an elemental substance, an alloy, anoxide, and an alloy with lithium is preferred because the batterycapacity may be increased. Above all, more preferred are thosecontaining at least one element selected from Si, Ge, and Sn, and stillmore preferred are those containing at least one element selected fromSi and Sn, as capable of increasing the battery capacity.

The negative electrode may be produced in such a manner that the sameelectroconductive agent, binder, and high-boiling point solvent as inthe production of the aforementioned positive electrode are used andkneaded to provide a negative electrode mixture, and this negativeelectrode mixture is then applied onto a collector, such as a copperfoil, etc., dried, shaped under pressure, and then heat-treated invacuum at a temperature of from about 50 to 250° C. for about 2 hours.

A density of a portion of the negative electrode except for thecollector is generally 1.1 g/cm³ or more, and for the purpose of furtherincreasing the capacity of the battery, the density is preferably 1.5g/cm³ or more, and more preferably 1.7 g/cm³ or more. Its upper limit ispreferably 2 g/cm³ or less.

Examples of the negative electrode active material for a lithium primarybattery include a lithium metal and a lithium alloy.

The structure of the lithium battery is not particularly limited, andmay be a coin-type battery, a cylinder-type battery, a prismaticbattery, a laminate-type battery, or the like, each having asingle-layered or multi-layered separator.

Although the separator for the battery is not particularly limited, asingle-layered or laminated micro-porous film of a polyolefin, such aspolypropylene, polyethylene, etc., as well as a woven fabric, a nonwovenfabric, etc., may be used.

The lithium secondary battery of the present invention has excellentelectrochemical characteristics in a broad temperature range even whenthe final charging voltage is 4.2 V or more, and particularly 4.3 V ormore, and furthermore, the characteristics thereof are still good evenat 4.4 V or more. Although the final discharging voltage may begenerally 2.8 V or more, and further 2.5 V or more, the finaldischarging voltage of the lithium secondary battery of the presentinvention may be 2.0 V or more. Although a current value is notspecifically limited, in general, the battery is used within the rangeof from 0.1 to 30 C. The lithium battery of the present invention may becharged/discharged at from-40 to 100° C., and preferably at from-10 to80° C.

In the present invention, as a countermeasure against an increase in theinternal pressure of the lithium battery, such a method may be adoptedthat a safety valve is provided in the battery cap, and a cutout isprovided in the battery component, such as a battery can, a gasket, etc.As a safety countermeasure for preventing overcharging, a currentcut-off mechanism capable of detecting an internal pressure of thebattery to cut off the current may be provided in a battery cap.

[Secondary Energy Storage Device (Electric Double Layer Capacitor)]

The secondary energy storage device is an energy storage device thatstores energy by utilizing the electric double layer capacitance in theinterface between the electrolytic solution and the electrode therein.One example of the present invention is an electric double layercapacitor. The most typical electrode active material to be used in thisenergy storage device is active carbon. The double-layer capacitanceincreases almost in proportion to the surface area.

[Third Energy Storage Device]

The third energy storage device is an energy storage device that storesenergy by utilizing the doping/dedoping reaction of the electrodetherein. As the electrode active material for use in this energy storagedevice, there may be mentioned metal oxides, such as ruthenium oxide,iridium oxide, tungsten oxide, molybdenum oxide, copper oxide, etc.; andπ-conjugated polymers, such as polyacene, polythiophene derivatives,etc. The capacitor that uses such an electrode active material enablesenergy storage along with the doping/dedoping reaction at the electrodetherein.

[Fourth Energy Storage Device (Lithium Ion Capacitor)]

The fourth energy storage device is an energy storage device that storesenergy by utilizing intercalation of a lithium ion into a carbonmaterial, such as graphite, etc., servicing as the negative electrode.This energy storage device may also be referred to as a lithium ioncapacitor (LIC). Examples of the positive electrode include oneutilizing an electric double layer between an active carbon electrodeand an electrolytic solution therein, one utilizing doping/dedopingreaction of a π-conjugated polymer electrode. The electrolytic solutioncontains at least a lithium salt, such as LiPF₆, etc.

In the aforementioned constitutional examples of energy storage devices,an example (first embodiment) containing at least one selected from theSO₄ group-containing compounds represented by any one of the generalformulae (I) to (IV) in an electrolytic solution has been explained;however, the compound may also be contained in other energy storagedevice constitutional element than the electrolytic solution.

In second to fourth embodiments as explained below, examples of energystorage devices in which at least one selected from the SO₄group-containing compounds represented by any one of the generalformulae (I) to (IV) (hereinafter also referred to as “additive of thepresent invention”) is previously added to other constitutional elementthan the electrolytic solution are explained.

Second Embodiment Example in which the Additive of the Present Inventionis Added to a Positive Electrode

The positive electrode may be produced by mixing the additive of thepresent invention with the aforementioned positive electrode activematerial, an electroconductive agent and a binder, adding a high-boilingpoint solvent, such as 1-methyl-2-pyrrolidone, etc., thereto, followedby kneading to prepare a positive electrode mixture, applying thispositive electrode mixture onto a collector, such as an aluminum foil, astainless steel-made lath plate, etc., and drying and shaping theresultant under pressure, followed by a heat treatment in vacuum at atemperature of from about 50° C. to 250° C. for about 2 hours.

An addition amount of the additive of the present invention ispreferably 0.001 to 5% by mass relative to the positive electrode activematerial. The addition amount is more preferably 0.05% by mass or more,and still more preferably 0.1% by mass or more relative to the positiveelectrode active material. Its upper limit is more preferably 3% by massor less, and still more preferably 1% by mass or less.

Third Embodiment Example in which the Additive of the Present Inventionis Added to a Negative Electrode

The negative electrode may be produced in such a manner that theadditive of the present invention with the same electroconductive agent,binder, and high-boiling point solvent as in the production of theaforementioned positive electrode are used and kneaded to provide anegative electrode mixture, and this negative electrode mixture is thenapplied onto a collector, such as a copper foil, etc., dried, shapedunder pressure, and then heat-treated in vacuum at a temperature of fromabout 50 to 250° C. for about 2 hours.

An addition amount of the additive of the present invention ispreferably 0.001 to 5% by mass relative to the negative electrode activematerial. The addition amount is more preferably 0.05% by mass or more,and still more preferably 0.1% by mass or more relative to the negativeelectrode active material. Its upper limit is more preferably 3% by massor less, and still more preferably 1% by mass or less.

Fourth Embodiment Example in which the Additive of the Present Inventionis Added to a Separator

The separator in which the additive of the present invention iscontained in a surface or pores thereof may be produced by a method ofimmersing and impregnating a separator in a solution having the additiveof the present invention dissolved in an organic solvent or water,followed by drying. The separator may also be produced by preparing acoating solution having the additive of the present invention dispersedin an organic solvent or water and applying the coating solution ontothe entire surface of the separator.

[Novel Compounds]

One of the SO₄ group-containing compounds that are a novel compound inthe present invention is represented by the following general formula(I-4):

wherein R²¹ is a straight-chain or branched alkenyl group having 3 to 7carbon atoms, a straight-chain or branched alkynyl group having 3 to 8carbon atoms, a linear or cyclic ester group having 3 to 18 carbonatoms, a linear or cyclic carbonate group having 3 to 18 carbon atoms, asulfur atom-containing organic group having 1 to 6 carbon atoms, asilicon atom-containing organic group having 4 to 10 carbon atoms, acyano group-containing organic group having 2 to 7 carbon atoms, aphosphorus atom-containing organic group having 2 to 12 carbon atoms, a—P(═O)F₂ group, an alkylcarbonyl group having 2 to 7 carbon atoms, or anarylcarbonyl group having 7 to 13 carbon atoms.

Specific examples of R²¹ are the same as the specific examples of L¹² inthe foregoing general formula (I-2), except that a vinyl group is notincluded.

Specifically, with respect to the compound represented by the generalformula (I-4), there are suitably exemplified the same compounds asthose represented by the foregoing general formula (I-2), except thatCompound AA1 described in [Chem. 16] is not included.

The compound represented by the general formula (I-4) may be synthesizedby the following (P1) or (P2) method, but the synthesis method is notlimited to these methods.

(P1) A method in which an alcohol compound and chlorosulfonic acid areallowed to react with each other, followed by performing a reaction witha lithium salt, such as lithium chloride, lithium acetate, etc.

(P2) A method in which lithium chlorosulfonate which has been previouslysynthesized from chlorosulfonic acid and lithium chloride is allowed toreact with a corresponding alcohol compound.

Other SO₄ group-containing compounds that are a novel compound arerepresented by the following general formula (II-1):

wherein R²¹ represents a p-valent hydrocarbon connecting group which maycontain a thioether bond or an —S(═O)₂— bond; and p is an integer of 2to 4, provided that in R²¹, at least one hydrogen atom which R²¹ has maybe substituted with a halogen atom.

Specific examples of R²¹ are the same as the specific examples of L² inthe foregoing general formula (II), except that an ether bond is notincluded.

In the foregoing general formula (II-1), p is preferably 2 or 3, andmore preferably 2.

Specifically, with respect to the compound represented by the generalformula (II-1), there are suitably exemplified the same compounds asthose represented by the foregoing general formula (II), except thatCompounds BA33 to 36 described in [Chem. 32] are not included.

The lithium compound of the present invention may be synthesized by theaforementioned (P1) or (P2) method, but the synthesis method is notlimited to these methods.

Other SO₄ group-containing compounds that are a novel compound arerepresented by the following general formula (III-3) or (IV-2);

wherein L³³ represents a t-valent hydrocarbon connecting group which maycontain a thioether bond or an —S(═O)₂— bond, t is an integer of 2 to 4,provided that in L³³, at least one hydrogen atom may be substituted witha halogen atom, and L³³ represents a group other than a2,2,3,3-tetrafluorobutane-1,4-diyl group, and

each of R³¹ to R³³ independently represents an alkyl group having 1 to12 carbon atoms, an alkenyl group having 2 to 3 carbon atoms, or an arylgroup having 6 to 8 carbon atoms.

Specific examples of L³³ in the general formula (III-3) are the same asthe specific examples of L² in the general formula (II) within the rangeof the aforementioned definition, and specific examples of R³¹ to R³³ inthe general formula (III-3) are the same as the specific examples of R³¹to R³³ in the general formula (III-1) within the range of theaforementioned definition.

wherein L⁴¹ represents an alkyl group having 1 to 12 carbon atoms, analkenyl group having 2 to 6 carbon atoms, an alkynyl group having 3 to 6carbon atoms, an alkoxyalkyl group having 2 to 12 carbon atoms, a—CR⁴¹R⁴²C(═O)OR⁴³ group, or an aryl group having 6 to 12 carbon atoms,X² represents an SiR³¹R³²R³³ group or an SiR⁴⁴R⁴⁵ group, and r is aninteger of 1 or 2,

provided that when X² is an SiR³¹R³²R³³ group, then r is 1, and L⁴¹ isan alkyl group having 2 to 8 carbon atoms, a 2,2,3,3-terafluoropropylgroup, an alkenyl group having 2 to 6 carbon atoms, an alkoxyalkyl grouphaving 2 to 12 carbon atoms, a —CR⁴¹R⁴²C(═O)OR⁴³ group, or an aryl grouphaving 6 to 12 carbon atoms, and when X² is an SiR⁴⁴R⁴⁵ group, then r is2,

each of R⁴¹ and R⁴² independently represents a hydrogen atom or an alkylgroup having 1 to 4 carbon atoms, R⁴³ represents an alkyl group having 1to 8 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or analkynyl group having 3 to 6 carbon atoms, and each of R³¹ to R³³, R⁴⁴,and R⁴⁵ independently represents an alkyl group having 1 to 12 carbonatoms, an alkenyl group having 2 to 3 carbon atoms, or an aryl grouphaving 6 to 8 carbon atoms, and is not bonded to each other to form aring, and

in the alkyl group and the aryl group, at least one hydrogen atom may besubstituted with a halogen atom.

In the general formula (IV-2), specific examples of L⁴¹, R⁴¹ to R⁴³, X²,R⁴⁴, and R⁴⁵ are the same as the specific examples of L⁴, R⁴¹ to R⁴³, X,R⁴⁴, and R⁴⁵ in the general formula (IV).

In the general formula (IV-2), specific examples of R³¹ to R³³ are thesame as the specific examples of R³¹ to R³³ in the general formula(III-2) within the range of the aforementioned definition.

The compounds represented by the general formula (III-3) or (IV-2) maybe, for example, synthesized by allowing chlorosulfonic acid, analcohol, and a halogenated silyl compound to react with each other, butthe synthesis method is not limited to such a method. For example,reference may be made to a method described in Bull. Chem. Soc. Jpn.,74, 181-182 (2001).

In the aforementioned method, there are exemplified a method in whichchlorosulfonic acid and an alcohol are allowed to react with each otherin the presence or absence of a solvent, followed by performing areaction with a halogenated silyl compound; and a method in whichchlorosulfonic acid and a halogenated silyl compound are allowed toreact with each other in the presence or absence of a solvent, followedby performing a reaction with an alcohol. However, the order of thesereactions is not limited at all.

As for use amounts of the raw materials to be used for the reaction, amolar number of the halogenated silyl compound is preferably 1 to 2times, and more preferably 1.2 to 1.7 times a molar number ofchlorosulfonic acid or the alcohol, whichever is larger. This is becauseif the halogenated silyl compound is insufficient, and a sulfonic acidgroup remains in the system, a side reaction is liable to proceed duringthe purification.

In the case of using a solvent, an alkyl halide solvent, such asdichloromethane, 1,2-dichloroethane, etc., is preferred. An amount ofthe solvent is preferably 1 to 10 parts by mass, and more preferably 2to 5 parts by mass based on 1 part by mass of the chlorosulfonic acid.

Although a reaction temperature varies depending upon a boiling point ormelting point of the solvent, it is preferably −10° C. to 85° C., andmore preferably 0° C. to 60° C.

Although a reaction time also varies depending upon the reactiontemperature and an amount of the produced HCl gas, it is preferably 30minutes to 5 hours, and more preferably 1 hour to 3 hours.

EXAMPLES

Synthesis Examples of the compounds to be used in the present inventionand Examples of an electrolytic solution using the SO₄ group-containingcompound of the present invention are hereunder described, but it shouldnot be construed that the present invention is limited to theseExamples.

<SO₄ Group-Containing Compound Represented by the General Formula (I-1)>Examples I-1 to I-37 and Comparative Examples I-1 to I-3 Production ofLithium Ion Secondary Battery

94% by mass of LiCoO₂ and 3% by mass of acetylene black(electroconductive agent) were mixed and then added to and mixed with asolution which had been prepared by dissolving 3% by mass ofpolyvinylidene fluoride (binder) in 1-methyl-2-pyrrolidone in advance,thereby preparing a positive electrode mixture paste. This positiveelectrode mixture paste was applied onto one surface of an aluminum foil(collector), dried, and treated under pressure, followed by cutting intoa predetermined size, thereby producing a positive electrode sheet. Adensity of a portion of the positive electrode except for the collectorwas 3.6 g/cm³.

95% by mass of artificial graphite (d₀₀₂=0.335 nm, negative electrodeactive material) was added to and mixed with a solution which had beenprepared by dissolving 5% by mass of polyvinylidene fluoride (binder) in1-methyl-2-pyrrolidone in advance, thereby preparing a negativeelectrode mixture paste. This negative electrode mixture paste wasapplied onto one surface of a copper foil (collector), dried, andtreated under pressure, followed by cutting into a predetermined size,thereby producing a negative electrode sheet. A density of a portion ofthe negative electrode except for the collector was 1.5 g/cm³.

This electrode sheet was analyzed by means of X-ray diffraction, and asa result, a ratio [I(110)/I(004)] of a peak intensity I(110) of the(110) plane to a peak intensity I(004) of the (004) plane of thegraphite crystal was found to be 0.1.

The above-obtained positive electrode sheet, a micro-porous polyethylenefilm-made separator, and the above-obtained negative electrode sheetwere laminated in this order, and a nonaqueous electrolytic solutionhaving each of compositions shown in Tables 1 to 3 was added thereto,thereby producing 2032 coin-type batteries.

[Evaluation of Low-Temperature Properties after High-TemperatureCharging Storage]

<Initial Discharge Capacity>

In a thermostatic chamber at 25° C., each of the coin-type batteriesproduced by the aforementioned method was charged up to a final voltageof 4.2 V with a constant current of 1 C and under a constant voltage for3 hours; the temperature of the thermostatic chamber was then decreasedto −10° C.; and the battery was discharged down to a final voltage of2.75 V with a constant current of 1 C, thereby determining an initialdischarge capacity at −10° C.

<High-Temperature Charging Storage Test>

Subsequently, in a thermostatic chamber at 85° C., this coin-typebattery was charged up to a final voltage of 4.2 V with a constantcurrent of 1 C and under a constant voltage for 3 hours and then storedfor 3 days in a state of keeping at 4.2 V. Thereafter, the resultant wasput in a thermostatic chamber at 25° C. and then once discharged down toa final voltage of 2.75 V with a constant current of 1 C.

<Discharge Capacity after High-Temperature Charging Storage>

Furthermore, a discharge capacity at −10° C. after the high-temperaturecharging storage was then determined in the same manner as themeasurement of the initial discharge capacity.

<Low-Temperature Properties after High-Temperature Charging Storage>

The low-temperature properties after the high-temperature chargingstorage were determined from the following discharge capacity retentionrate at −10° C.

Discharge capacity retention rate (%) at −10° C. after high-temperaturecharging storage=(Discharge capacity at −10° C. after high-temperaturecharging storage)/(Initial discharge capacity at −10° C.)×100

<High-Temperature Cycle Properties>

In a thermostatic chamber at 55° C., each of the batteries produced bythe aforementioned method was treated by repeating a cycle of chargingup to a final voltage of 4.2 V with a constant current of 1 C and undera constant voltage for 3 hours and subsequently discharging down to adischarge voltage of 3.0 V with a constant current of 1 C, until itreached 300 cycles. Then, a discharge capacity retention rate after thecycles was determined according to the following equation.

Discharge capacity retention rate (%)=(Discharge capacity after 300cycles)/(Discharge capacity after 1st cycle)×100

The results are shown in Tables 1 to 3.

TABLE 1 Discharge Composition of SO₄ group-containing compound (I)capacity electrolyte salt Content in retention rate at Composition ofnonaqueous −10° C. after nonaqueous electrolytic electrolytichigh-temperature solution solution charging storage (Volume ratio ofsolvent) Compound (% by mass) at 85° C. (%) Example I-1 1.15 M LiPF₆EC/DMC/MEC (30/45/25)

0.3  75 Example 1.15 M LiPF₆ 0.3  70 I-2 EC/MEC (30/70) Example 1.15 MLiPF₆ 0.005 71 I-3 EC/VC/DMC/MEC (29/1/40/30) Example 1.15 M LiPF₆ 0.1 78 I-4 EC/VC/DMC/MEC (29/1/40/30) Example 1.15 M LiPF₆ 0.3  80 I-5EC/VC/DMC/MEC (29/1/40/30) Example 1.15 M LiPF₆ 0.5  76 I-6EC/VC/DMC/MEC (29/1/40/30) Example 1.15 M LiPF₆ 1    73 I-7EC/VC/DMC/MEC (29/1/40/30) Example 1.15 M LiPF₆ 3    71 I-8EC/VC/DMC/MEC (29/1/40/30)

TABLE 2 Composition of SO₄ group-containing compound (I) Dischargecapacity Discharge electrolyte salt Content in retention rate atcapacity Composition of nonaqueous −10° C. after retention ratenonaqueous electrolytic electrolytic high-temperature after 300 solutionsolution (% by charging storage at cycles at 55° C. (Volume ratio ofsolvent) Kind mass) 85° C. (%) (%) Example I-9 1.1 M LiPF₆ EC/VC/DMC/MEC(29/1/45/25)

0.3 79 76 Example I-10 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

0.3 78 75 Example I-11 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

0.3 78 75 Example I-12 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

0.3 75 72 Example I-13 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

0.3 74 68 Example I-14 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

0.3 73 68 Example I-15 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

0.3 75 70 Example I-16 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

0.3 79 75 Example I-17 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

0.3 79 75 Example I-18 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

0.3 77 72 Example I-19 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

0.3 78 71 Example I-20 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

0.3 82 79 Example I-21 1.1 M LiPF₆ + 0.05 M LiBOB EC/FEC/VC/DMC/MEC(19/10/1/45/25)

0.3 85 80 Example I-22 1.1 M LiPF₆ + 0.05 M LiPO₂F₂ EC/FEC/VC/DMC/MEC(19/10/1/45/25)

0.3 84 78 Example I-23 1.1 M LiPF₆ + 0.05 M LiPFO EC/FEC/VC/DMC/MEC(19/10/1/45/25)

0.3 85 81 Example I-24 0.7 M LiPF₆ + 0.45 M LiFSI EC/VC/DMC/MEC(29/1/45/25)

0.3 86 80

TABLE 3 Discharge Composition of SO₄ group-containing capacityelectrolyte salt compound (I) retention rate Discharge Composition ofContent in at −10° C. after capacity nonaqueous nonaqueous Otheradditive (content high-temperature retention rate electrolytic solutionelectrolytic Other in nonaqueous charging after 300 (Volume ratio ofsolution additive electrolytic solution (% storage at cycles at 55° C.solvent) Compound (% by mass) group by mass)) 85° C. (%) (%) ExampleI-25 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

0.3 A Adiponitrile (1) 83 75 Example B Cyclohexylbenzene (2) + 82 72I-26 o-terphenyl (1) Example C 1,6-Hexamethylene 84 77 I-27 diisocycnate(0.5) Example C 1,6-Hexamethylene 82 75 I-28 diisocycnate (0.5) ExampleD 2-Butyne-1,4-diyl 85 79 I-29 dimethanesulfonate (0.5) Example D2-Butyne-1,4-diyl 82 78 I-30 dimethanesulfonate (1) Example E2,4-Butanesultone (1) 84 76 I-31 Example E 5,5-Dimethyl- 85 75 I-321,2-oxathiolane-4-one 2,2-dioxide (0.5) Example F 1,3-Dioxane (1) 81 73I-33 Example G Tris(2,2,2-trifluoroethyl) 83 77 I-34 phosphate (1.5)Example H Succinic anhydride (1) 83 78 I-35 Example I Ethoxypentafluoro-82 73 I-36 cyclotriphosphazene (1) Example J Trimethylsilyl 85 76 I-37fluorosulfonate (1) Comparative None — — — 62 67 Example I-1 ComparativeExample I-2

0.3 — — 61 68 Comparative Example I-3 1.1 M LiPF₆ EC/VC/DMC/MEC(29/1/45/25)

0.3 — — 55 62

Examples I-38 to I-39 and Comparative Example I-4

A negative electrode sheet was produced by using silicon (elementalsubstance) (negative electrode active material) in place of the negativeelectrode active material used in Example I-1. 80% by mass of silicon(elemental substance) and 15% by mass of acetylene black(electroconductive agent) were mixed and then added to and mixed with asolution which had been prepared by dissolving 5% by mass ofpolyvinylidene fluoride (binder) in 1-methyl-2-pyrrolidone in advance,thereby preparing a negative electrode mixture paste. Coin-typebatteries were produced in the same manner as in Example I-1, exceptthat this negative electrode mixture paste was applied onto the surfaceof a copper foil (collector), dried, and treated under pressure,followed by cutting into a predetermined size, thereby producing anegative electrode sheet, and that the composition of the nonaqueouselectrolytic solution was changed to a predetermined composition, andthe batteries were evaluated. The results are shown in Table 4.

TABLE 4 Composition of SO₄ group-containing Discharge electrolyte saltcompound (I) capacity Composition of Content in Other additive retentionrate at nonaqueous nonaqueous (content in −10° C. after electrolyticsolution electrolytic Other nonaqueous high-temperature (Volume ratio ofsolution additive electrolytic solution charging storage solvent) Kind(% by mass) group (% by mass)) at 85° C. (%) Example I-33 1.2 M LiPF₆PC/FEC/DMC/MEC (15/15/45/25)

0.3 — — 70 Example C 1,6-Hexamethylene 75 I-39 diisocyanate (0.5)Comparative None — — — 47 Example I-4

Examples I-40 to I-41 and Comparative Example I-5

A negative electrode sheet was produced by using lithium titanateLi₄Ti₅O₁₂ (negative electrode active material) in place of the negativeelectrode active material used in Example I-1. 80% by mass of lithiumtitanate Li₄Ti₅O₁₂ and 15% by mass of acetylene black (electroconductiveagent) were mixed and then added to and mixed with a solution which hadbeen prepared by dissolving 5% by mass of polyvinylidene fluoride(binder) in 1-methyl-2-pyrrolidone in advance, thereby preparing anegative electrode mixture paste. Coin-type batteries were produced inthe same manner as in Example I-1, except that this negative electrodemixture paste was applied onto a copper foil (collector), dried, andtreated under pressure, followed by cutting into a predetermined size,thereby producing a negative electrode sheet; that in evaluating thebattery, the final charging voltage and the final discharging voltagewere set to 2.8 V and 1.2 V, respectively; and that the composition ofthe nonaqueous electrolytic solution was changed to a predeterminedcomposition, and the batteries were evaluated. The results are shown inTable 5.

TABLE 5 Composition of SO₄ group-containing Discharge electrolyte saltcompound (I) capacity Composition of Content in Other additive retentionrate at nonaqueous nonaqueous (content in −10° C. after electrolyticsolution electrolytic Other nonaqueous high-temperature (Volume ratio ofsolution additive electrolytic solution charging storage solvent) Kind(% by mass) group (% by mass)) at 85° C. (%) Example I-40 1.2 M LiPF₆PC/DEC (30/70)

0.3 — — 85 Example D Di(2-propynyl) 88 I-41 oxalate (0.5) ComparativeNone — — — 64 Example I-5

Example I-42 and Comparative Example I-6

A positive electrode sheet was produced by using LiFePO₄ (positiveelectrode active material) coated with amorphous carbon in place of thepositive electrode active material used in Example I-1. 90% by mass ofLiFePO₄ coated with amorphous carbon and 5% by mass of acetylene black(electroconductive agent) were mixed and then added to and mixed with asolution which had been prepared by dissolving 5% by mass ofpolyvinylidene fluoride (binder) in 1-methyl-2-pyrrolidone in advance,thereby preparing a positive electrode mixture paste. Coin-typebatteries were produced in the same manner as in Example I-1, exceptthat this positive electrode mixture paste was applied onto an aluminumfoil (collector), dried, and treated under pressure, followed by cuttinginto a predetermined size, thereby producing a positive electrode sheet;that in evaluating the battery, the final charging voltage and the finaldischarging voltage were set to 3.6 V and 2.0 V, respectively; and thatthe composition of the nonaqueous electrolytic solution was changed to apredetermined composition, and the batteries were evaluated. The resultsare shown in Table 6.

TABLE 6 Composition of SO₄ group-containing Discharge electrolyte saltcompound (I) capacity Composition of Content in Other additive retentionrate at nonaqueous nonaqueous (content in −10° C. after electrolyticsolution electrolytic Other nonaqueous high-temperature (Volume ratio ofsolution additive electrolytic solution charging storage solvent) Kind(% by mass) group (% by mass)) at 85° C. (%) Example I-42 1.2 M LiPF₆EC/VC/DMC/MEC (29/1/45/25)

0.3 — — 82 Comparative None — — — 59 Example I-6

Example I-43 and Comparative Examples I-7 and I-8

Positive electrode sheets were produced by using LiNi_(1/2)Mn_(3/2)O₄(positive electrode active material) in place of the positive electrodeactive materials used in Examples I-1, Comparative Example I-1, andComparative Example I-3, respectively. 94% by mass ofLiNi_(1/2)Mn_(3/2)O₄ and 3% by mass of acetylene black(electroconductive agent) were mixed and then added to and mixed with asolution which had been prepared by dissolving 3% by mass ofpolyvinylidene fluoride (binder) in 1-methyl-2-pyrrolidone in advance,thereby preparing a positive electrode mixture paste. Coin-typebatteries were produced in the same manner as in Example I-1 andComparative Example I-1, respectively, except that this positiveelectrode mixture paste was applied onto one surface of an aluminum foil(collector), dried, and treated under pressure, followed by cutting intoa predetermined size, thereby producing a positive electrode sheet; andthat in evaluating the battery, the final charging voltage and the finaldischarging voltage were set to 4.9 V and 2.7 V, respectively, and thebatteries were evaluated.

An elution amount of Mn after the high-temperature charging storage wasdetermined by quantitatively determining an amount of manganese (Mn)electrodeposited on the negative electrode by the inductively coupledplasma atomic emission spectrophotometry. As for the elution amount ofMn, a relative elution amount of Mn was examined on the basis ofdefining the elution amount of Mn of Comparative Example I-1 as 100%.The results are shown in Table 7.

TABLE 7 Composition of electrolyte salt SO₄ group-containing compound(I) Discharge capacity Relative elution Composition of Content inretention rate at amount of Mn nonaqueous nonaqueous −10° C. after afterelectrolytic solution electrolytic high-temperature high-temperature(Volume ratio of solution charging storage at charging storage solvent)Kind (% by mass) 85° C. (%) at 85° C. (%) Example I-43 1.15 M LiPF₆EC/FEC/MEC/DEC (20/10/45/25)

0.3 67  99 Comparative None — 48 100 Example I-7 Comparative Example I-8

0.3 33 250

Example I-44

A lithium secondary battery was produced in the same manner as inComparative Example I-1, except that a positive electrode produced byadding a predetermined amount of the SO₄ group-containing compoundrepresented by the general formula (I-1) relative to 100% of thepositive electrode active material was used. The results are shown inTable 8.

Example I-45

A lithium secondary battery was produced in the same manner as inExample I-44, except that the SO₄ group-containing compound representedby the general formula (I-1) was not added to the positive electrode butadded to the negative electrode. The results are shown in Table 8.

TABLE 8 Composition of Discharge electrolyte salt capacity Compositionof retention rate at nonaqueous SO₄ group-containing compound (I) −10°C. after electrolytic solution Content relative to high-temperature(Volume ratio of the active material charging storage solvent) KindAddition site (% by mass) at 85° C. (%) Example I-44 1.2 M LiPF₆EC/VC/DMC/MEC (29/1/45/25)

Positive electrode 0.3 77 Example Negative 0.3 79 I-45 electrode

In all of the lithium secondary batteries of Examples I-1 to I-37, theelectrochemical characteristics in a broad temperature range areremarkably improved as compared with the lithium secondary batteries ofComparative Example I-1 in the case of not adding the SO₄group-containing compound represented by the general formula (I),especially the general formula (I-1), Comparative Example I-2 in thecase of adding dimethyl sulfate, and Comparative Example I-3 in the caseof adding monomethyl sulfate, in the nonaqueous electrolytic solution ofthe present invention. In the light of the above, it has been clarifiedthat the effect of the present invention is a peculiar effect to thecase where the SO₄ group-containing compound specified in the presentinvention is contained in the nonaqueous electrolytic solution having anelectrolyte salt dissolved in a nonaqueous solvent. In addition, thedischarge capacity retention rate of the lithium secondary batteryproduced under the same conditions as those in Example I-5 exhibitedafter 300 cycles at 55° C. is 70%, that is, as well as in Examples I-25to I-37, the discharge capacity retention rate after 300 cycles at 55°C. was remarkably improved as compared with Comparative Examples I-1 toI-3.

From comparison of Examples I-38 to I-39 with Comparative Example I-4,comparison of Examples I-40 to I-41 with Comparative Example I-5,comparison of Example I-42 with Comparative Example I-6, and comparisonof Example I-43 with Comparative Example I-7, the same effect is alsoseen even in the case of using silicon (elemental substance) Si orlithium titanate for the negative electrode, or the case of using alithium-containing olivine-type iron phosphate or a lithium complexmetal oxide capable of being used at 4.4 V or more for the positiveelectrode, and therefore, it is evident that the effect of the presentinvention is not an effect relying on a specified positive electrode ornegative electrode.

Furthermore, from comparison of Example I-43 with Comparative ExampleI-8, it is understood that in the case of adding monomethyl sulfate, theelution of Mn is accelerated, so that the electrochemicalcharacteristics in a broad temperature range are remarkably worsened.

From comparison of Examples I-44 and I-45 with Comparative Example I-1,even in the case of containing the SO₄ group-containing compoundrepresented by the general formula (I), especially the general formula(I-1) in a site other than the electrolytic solution, the effect isbrought.

Moreover, the nonaqueous electrolytic solution of the present inventionalso has an effect for improving discharging properties of a lithiumprimary battery in a broad temperature range.

<SO₄ Group-Containing Compound Represented by the General Formula (I-2)>Synthesis Example II-1 Synthesis of Lithium 2-Cyanoethyl Sulfate(Compound AG2)

To a slurry mixed liquid of 4.24 g (100 mmoles) of lithium chloride and100 g of dimethyl carbonate, 11.65 g (100 mmoles) of chlorosulfonic acidwas added dropwise at 10° C. or lower over 15 minutes. After stirring atroom temperature for 60 minutes, 7.11 g (100 mmoles) of cyanoethanol wasadded dropwise. After stirring this solution at room temperature for 3hours, a crystal was separated by filtration from a reaction solutionbeing a slurry form and dried, thereby obtaining 13.35 g of lithium2-cyanoethyl sulfate as a white crystal (yield: 85%).

The obtained lithium 2-cyanoethyl sulfate was subjected to ¹H-NMRmeasurement to confirm its structure. The results are shown below.

¹H-NMR (400 MHz, DMSO-d6): δ (ppm)=3.90 (t, J=6.08 Hz, 2H), 2.79 (t,J=6.08 Hz, 2H)

Synthesis Example II-2 Synthesis of Lithium Propargyl Sulfate (CompoundAB1)

The same operations as those in Synthesis Example II-1 were followed,except for using propargyl alcohol in place of the cyanoethanol, therebyobtaining lithium propargyl sulfate as a white crystal (yield: 83%).

The obtained lithium propargyl sulfate was subjected to ¹H-NMRmeasurement to confirm its structure. The results are shown below.

¹H-NMR (400 MHz, DMSO-d6): δ (ppm)=4.33 (d, J=2.52 Hz, 2H), 3.37 (t,J=2.52 Hz, 1H)

Synthesis Example II-3 Synthesis of Lithium1-Oxo-1-(2-propynyloxy)propan-2-yl Sulfate (Compound AC11)

The same operations as those in Synthesis Example II-1 were followed,except for using propargyl lactate in place of the cyanoethanol, therebyobtaining lithium 1-oxo-1-(2-propynyloxy)propan-2-yl sulfate as a whitecrystal (yield: 82%).

The obtained lithium 1-oxo-1-(2-propynyloxy)propan-2-yl sulfate wassubjected to ¹H-NMR measurement to confirm its structure. The resultsare shown below.

¹H-NMR (400 MHz, DMSO-d6); δ (ppm)=4.70 (m, 2H), 4.57 (q, J=6.88 Hz,1H), 3.55 (t, J=2.44 Hz, 1H), 1.30 (d, J=6.88 Hz, 3H)

Synthesis Example II-4 Synthesis of Lithium Difluorophosphoryl Sulfate(Compound AH15)

To a slurry mixed liquid of 8.90 g (82 mmoles) of lithiumdifluorophosphate and 100 g of dimethyl carbonate, 9.15 g (78 mmoles) ofchlorosulfonic acid was added dropwise at 10° C. or lower over 15minutes. This solution was stirred at room temperature for 3 hours andconcentrated with an evaporator until the amount reached 60 g, and acrystal was separated by filtration. The obtained filtrate wasconcentrated and dried to obtain 9.00 g of lithium difluorophosphorylsulfate as a white crystal (yield: 61%).

The obtained lithium difluorophosphoryl sulfate was subjected to ¹⁹F-NMRmeasurement to confirm its structure. The results are shown below.

¹⁹F-NMR (400 MHz, DMSO-d6): δ (ppm)=−80.83 (d, J=944 Hz, 2F)

Synthesis Example II-5 Synthesis of Lithium Dibutoxyphosphoryl Sulfate(Compound AH10)

The same operations as those in Synthesis Example II-4 were followed,except for using lithium dibutylphosphate in place of the lithiumdifluorophosphate, thereby obtaining lithium dibutoxyphosphoryl sulfateas a white crystal (yield: 72%).

The obtained lithium dibutoxyphosphoryl sulfate was subjected to ¹H-NMRmeasurement to confirm its structure. The results are shown below.

¹H-NMR (400 MHz, DMSO-d6): δ (ppm)=3.86 (q, J=6.52 Hz, 2H), 1.59 to 1.52(m, 2H), 1.38 to 1.13 (m, 2H), 0.88 (t, J=7.40 Hz, 3H)

Examples II-1 to II-21 and Comparative Examples II-1 and II-2 Productionof Lithium Ion Secondary Battery

94% by mass of LiCoO₂ and 3% by mass of acetylene black(electroconductive agent) were mixed and then added to and mixed with asolution which had been prepared by dissolving 3% by mass ofpolyvinylidene fluoride (binder) in 1-methyl-2-pyrrolidone in advance,thereby preparing a positive electrode mixture paste. This positiveelectrode mixture paste was applied onto one surface of an aluminum foil(collector), dried, and treated under pressure, followed by cutting intoa predetermined size, thereby producing a positive electrode sheet. Adensity of a portion of the positive electrode except for the collectorwas 3.6 g/cm³.

95% by mass of artificial graphite (d₀₀₂=0.335 nm, negative electrodeactive material) was added to and mixed with a solution which had beenprepared by dissolving 5% by mass of polyvinylidene fluoride (binder) in1-methyl-2-pyrrolidone in advance, thereby preparing a negativeelectrode mixture paste. This negative electrode mixture paste wasapplied onto one surface of a copper foil (collector), dried, andtreated under pressure, followed by cutting into a predetermined size,thereby producing a negative electrode sheet. A density of a portion ofthe negative electrode except for the collector was 1.5 g/cm³.

This electrode sheet was analyzed by means of X-ray diffraction, and asa result, a ratio [I(110)/I(004)] of a peak intensity I(110) of the(110) plane to a peak intensity I(004) of the (004) plane of thegraphite crystal was found to be 0.1.

The above-obtained positive electrode sheet, a micro-porous polyethylenefilm-made separator, and the above-obtained negative electrode sheetwere laminated in this order, and a nonaqueous electrolytic solutionhaving each of compositions shown in Tables 9 to 10 was added thereto,thereby producing 2032 coin-type batteries.

[Evaluation of Low-Temperature Properties after High-TemperatureCharging Storage]

<Initial Discharge Capacity>

In a thermostatic chamber at 25° C., each of the coin-type batteriesproduced by the aforementioned method was charged up to a final voltageof 4.2 V with a constant current of 1 C and under a constant voltage for3 hours; the temperature of the thermostatic chamber was then decreasedto −10° C.; and the battery was discharged down to a final voltage of2.75 V with a constant current of 1 C, thereby determining an initialdischarge capacity at −10° C.

<High-Temperature Charging Storage Test>

Subsequently, in a thermostatic chamber at 85° C., this coin-typebattery was charged up to a final voltage of 4.2 V with a constantcurrent of 1 C and under a constant voltage for 3 hours and then storedfor 3 days in a state of keeping at 4.2 V. Thereafter, the resultant wasput in a thermostatic chamber at 25° C. and then once discharged down toa final voltage of 2.75 V with a constant current of 1 C.

<Discharge Capacity after High-Temperature Charging Storage>

Furthermore, a discharge capacity at −10° C. after the high-temperaturecharging storage was then determined in the same manner as themeasurement of the initial discharge capacity.

<Low-Temperature Properties after High-Temperature Charging Storage>

The low-temperature properties after the high-temperature chargingstorage was determined from the following discharge capacity retentionrate at −10° C.

Discharge capacity retention rate (%) at −10° C. after high-temperaturecharging storage=(Discharge capacity at −10° C. after high-temperaturecharging storage)/(Initial discharge capacity at −10° C.)×100

<High-Temperature Cycle Properties>

In a thermostatic chamber at 55° C., each of the batteries produced bythe aforementioned method was treated by repeating a cycle of chargingup to a final voltage of 4.2 V with a constant current of 1 C and undera constant voltage for 3 hours and subsequently discharging down to adischarge voltage of 3.0 V with a constant current of 1 C, until itreached 300 cycles. Then, a discharge capacity retention rate after thecycles was determined according to the following equation.

Discharge capacity retention rate (%)=(Discharge capacity after 300cycles)/(Discharge capacity after 1st cycle)×100

The results are shown in Tables 9 to 10.

TABLE 9 Composition of electrolyte salt SO₄ group-containing compound(I) Discharge capacity Composition of Content in retention rate atnonaqueous nonaqueous −10° C. after electrolytic solution electrolytichigh-temperature (Volume ratio of Type of solution charging storage atsolvent) substituent L¹² Kind (% by mass) 85° C. (%) Example II-1 1.2 MLiPF₆ EC/DEC (30/70) (ii)

0.3 69 Example II-2 1.2 M LiPF₆ 0.3 73 EC/DEC/MEC (30/45/25) ExampleII-3 1.2 M LiPF₆ 0.1 75 EC/FEC/DEC/MEC (25/5/45/25) Example II-4 1.2 MLiPF₆ 0.3 78 EC/FEC/DEC/MEC (25/5/45/25) Example II-5 1.2 M LiPF₆ 3   70EC/FEC/DEC/MEC (25/5/45/25) Comparative 1.2 M LiPF₆ — None — 58 ExampleII-1 EC/FEC/DEC/MEC (25/5/45/25) Comparative Example II-2 1.2 M LiPF₆EC/FEC/DEC/MEC (25/5/45/25) —

0.3 57

TABLE 10 Composition of electrolyte salt SO₄ group-containing compound(I) Discharge capacity Composition of Content in retention rate atnonaqueous electrolytic nonaqueous −10° C. after solution Type ofelectrolytic high-temperature (Volume ratio of substituent solutioncharging storage at solvent) L¹² Kind (% by mass) 85° C. (%) ExampleII-6 1.2 M LiPF₆ EC/FEC/DEC/MEC (25/5/45/25) (i)

0.3 80 Example II-7 1.2 M LiPF₆ EC/FEC/DEC/MEC (25/5/45/25) (vii)

0.3 81 Example II-8 1.2 M LiPF₆ EC/FEC/DEC/MEC (25/5/45/25) (iv)

0.3 75 Example II-9 1.2 M LiPF₆ EC/FEC/DEC/MEC (25/5/45/25) (ii)

0.3 82 Example II-10 1.2 M LiPF₆ EC/FEC/DEC/MEC (25/5/45/25) (iii)

0.3 79 Example II-11 1.2 M LiPF₆ EC/FEC/DEC/MEC (25/5/45/25) (v)

0.3 71 Example II-12 1.2 M LiPF₆ EC/FEC/DEC/MEC (25/5/45/25) (viii)

0.3 70 Example II-13 1.2 M LiPF₆ EC/FEC/DEC/MEC (25/5/45/25) (vi)

0.3 72 Example II-14 1.2 M LiPF₆ EC/FEC/DEC/MEC (25/5/45/25) (ix)

0.3 71 Example II-15 1.2 M LiPF₆ EC/FEC/DEC/MEC (25/5/45/25) (vi)

0.3 70 Example II-16 1.2 M LiPF₆ EC/FEC/DEC/MEC (25/5/45/25) (viii)

0.3 73 Example II-17 1.2 M LiPF₆ EC/FEC/DEC/MEC (25/5/45/25) (viii)

0.3 75 Example II-18 1.1 M LiPF₆ + 0.05 M LiSO₃F EC/FEC/VC/DEC/MEC(19/10/1/45/25) (ii)

0.3 85 Example II-19 1.1 M LiPF₆ + 0.05 M LiPFO₂F₂ EC/FEC/VC/DEC/MEC(19/10/1/45/25) (ii)

0.3 84 Example II-20 1.1 M LiPF₆ + 0.05 M LiPFO EC/FEC/VC/DEC/MEC(19/10/1/45/25) (ii)

0.3 86 Example II-21 0.7 M LiPF₆ + 0.45 M LiTFSI EC/FEC/VC/DEC/MEC(19/10/1/45/25) (ii)

0.3 85

Example II-22 and Comparative Example II-3

A negative electrode sheet was produced by using silicon (elementalsubstance) (negative electrode active material) in place of the negativeelectrode active material used in Example II-1. 80% by mass of silicon(elemental substance) and 15% by mass of acetylene black(electroconductive agent) were mixed and then added to and mixed with asolution which had been prepared by dissolving 5% by mass ofpolyvinylidene fluoride (binder) in 1-methyl-2-pyrrolidone in advance,thereby preparing a negative electrode mixture paste. Coin-typebatteries were produced in the same manner as in Example II-1, exceptthat this negative electrode mixture paste was applied onto a copperfoil (collector), dried, and treated under pressure, followed by cuttinginto a predetermined size, thereby producing a negative electrode sheet,and that the composition of the nonaqueous electrolytic solution waschanged to a predetermined composition, and the batteries wereevaluated. The results are shown in Table 11.

TABLE 11 Composition Discharge electrolyte salt SO₄ group-containingcompound (I) capacity Composition of Content in retention rate atnonaqueous electrolytic nonaqueous −10° C. after solution electrolytichigh-temperature (Volume ratio of solution charging storage solvent)Kind (% by mass) at 85° C. (%) Example II-22 1.2 M LiPF₆ PC/FEC/DEC/MEC(10/20/45/25)

0.3 72 Comparative None — 52 Example II-3

Example II-23 and Comparative Example II-4

90% by mass of LiMn_(1.5)Ni_(0.5)O₄ and 6% by mass of acetylene black(electroconductive agent) were mixed and then added to and mixed with asolution which had been prepared by dissolving 4% by mass ofpolyvinylidene fluoride (binder) in 1-methyl-2-pyrrolidone in advance,thereby preparing a positive electrode mixture paste. This positiveelectrode mixture paste was applied onto one surface of an aluminum foil(collector), dried, and treated under pressure, followed by cutting intoa predetermined size, thereby producing a positive electrode sheet. 80%by mass of Li₄Ti₅O₁₂ (negative electrode active material) and 15% bymass of acetylene black (electroconductive agent) were mixed and thenadded to and mixed with a solution which had been prepared by dissolving5% by mass of polyvinylidene fluoride (binder) in 1-methyl-2-pyrrolidonein advance, thereby preparing a negative electrode mixture paste. Thisnegative electrode mixture paste was applied onto one surface of acopper foil (collector), dried, and treated under pressure, followed bycutting into a predetermined size, thereby producing a negativeelectrode sheet. Then, the positive electrode sheet, a micro-porouspolyethylene film-made separator, and the negative electrode sheet werelaminated in this order, and a nonaqueous electrolytic solution havingthe composition shown in Table 11 was added thereto, thereby producing2032 coin-type batteries.

The batteries were evaluated in the same manner as in Example II-1,except that in evaluating the battery, the final charging voltage andthe final discharging voltage were set to 3.5 V and 2.5 V, respectively;and that the composition of the nonaqueous electrolytic solution waschanged to a predetermined composition. The results are shown in Table12.

TABLE 12 Composition of Discharge electrolyte salt SO₄ group-containingcompound (I) capacity Composition of Content in retention rate atnonaqueous nonaqueous −10° C. after electrolytic solution electrolytichigh-temperature (Volume ratio of solution charging storage solvent)Kind (% by mass) at 85° C. (%) Example II-23 1.1 M LiPF₆ EC/DCM/MEC(30/40/30)

0.3 64 Comparative None — 45 Example II-4

Example II-24

A lithium secondary battery was produced in the same manner as inComparative Example II-1, except that a positive electrode produced byadding a predetermined amount of the SO₄ group-containing compoundrepresented by the general formula (I-2) relative to 100% of thepositive electrode active material was used. The results are shown inTable 13.

Example II-25

A lithium secondary battery was produced in the same manner as inExample II-24, except that the SO₄ group-containing compound representedby the general formula (I-2) was not added to the positive electrode butadded to the negative electrode. The results are shown in Table 13.

TABLE 13 Composition of Discharge electrolyte salt capacity Compositionof retention rate at nonaqueous SO₄ group-containing compound (I) −10°C. after electrolytic solution Content relative to high-temperature(Volume ratio of the active material charging storage solvent) KindAddition site (% by mass) at 85° C. (%) Example II-24 1.2 M LiPF₆EC/FEC/DEC/MEC (25/5/45/25)

Positive electrode 0.2 71 Example Negative 0.2 73 II-25 electrode

In all of the lithium secondary batteries of Examples II-1 to II-21, theelectrochemical characteristics in a broad temperature range areremarkably improved as compared with the lithium secondary batteries ofComparative Example II-1 in the case of not adding the SO₄group-containing compound represented by the general formula (I),especially the general formula (I-2) and Comparative Example II-2 in thecase of adding dimethyl sulfate, in the nonaqueous electrolytic solutionof the present invention. In the light of the above, it has beenclarified that the effect of the present invention is a peculiar effectto the case where the SO₄ group-containing compound specified in thepresent invention is contained in the nonaqueous electrolytic solutionhaving an electrolyte salt dissolved in a nonaqueous solvent. Inaddition, the discharge capacity retention rate of the lithium secondarybattery produced under the same conditions as those in Example II-4after 300 cycles at 55° C. is 68%, and the discharge capacity retentionrates of the lithium secondary batteries produced under the sameconditions as those in Comparative Example II-1 and Comparative ExampleII-2 after 300 cycles at 55° C. are 64% and 65%, respectively. Thus, thedischarge capacity retention rate after 300 cycles at 55° C. wasremarkably improved.

From comparison of Example II-22 with Comparative Example II-3 andcomparison of Example II-23 with Comparative Example II-4, the sameeffect is also seen even in the case of using silicon (elementalsubstance) Si or lithium titanate for the negative electrode, or thecase of using LiMn_(4.5)Ni_(0.5)O₄ for the positive electrode, andtherefore, it is evident that the effect of the present invention is notan effect relying on a specified positive electrode or negativeelectrode.

From comparison of Examples II-24 and II-25 with Comparative ExampleII-1, even in the case of containing the SO₄ group-containing compoundrepresented by the general formula (I), especially the general formula(I-2) in a site other than the electrolytic solution, the effect isbrought.

Furthermore, the nonaqueous electrolytic solution of the presentinvention also has an effect for improving discharging properties of alithium primary battery in a broad temperature range.

<SO₄ Group-Containing Compound Represented by the General Formula (I-3)>Examples III-1 to III-15 and Comparative Examples III-1 to III-2Production of Lithium Ion Secondary Battery

94% by mass of LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ and 3% by mass of acetyleneblack (electroconductive agent) were mixed and then added to and mixedwith a solution which had been prepared by dissolving 3% by mass ofpolyvinylidene fluoride (binder) in 1-methyl-2-pyrrolidone in advance,thereby preparing a positive electrode mixture paste. This positiveelectrode mixture paste was applied onto one surface of an aluminum foil(collector), dried, and treated under pressure, followed by cutting intoa predetermined size, thereby producing a positive electrode sheet. Adensity of a portion of the positive electrode except for the collectorwas 3.6 g/cm³.

95% by mass of artificial graphite (d₀₀₂=0.335 nm, negative electrodeactive material) was added to and mixed with a solution which had beenprepared by dissolving 5% by mass of polyvinylidene fluoride (binder) in1-methyl-2-pyrrolidone in advance, thereby preparing a negativeelectrode mixture paste. This negative electrode mixture paste wasapplied onto one surface of a copper foil (collector), dried, andtreated under pressure, followed by cutting into a predetermined size,thereby producing a negative electrode sheet. A density of a portion ofthe negative electrode except for the collector was 1.5 g/cm³.

This electrode sheet was analyzed by means of X-ray diffraction, and asa result, a ratio [I(110)/I(004)] of a peak intensity I(110) of the(110) plane to a peak intensity I(004) of the (004) plane of thegraphite crystal was found to be 0.1.

The above-obtained positive electrode sheet, a micro-porous polyethylenefilm-made separator, and the above-obtained negative electrode sheetwere laminated in this order, and a nonaqueous electrolytic solutionhaving each of compositions shown in Tables 14 to 15 was added thereto,thereby producing laminate-type batteries.

[High-Temperature Storage Test]

<Evaluation of Gas Generation Amount after High-Temperature Storage>

In a thermostatic chamber at 25° C., each of the laminate-type batteriesproduced by the aforementioned method was charged up to a final voltageof 4.35 V with a constant current of 1 C and under a constant voltageand then charged at a final voltage of 4.35 V under a constant voltagefor 7 hours in total. Subsequently, the battery was discharged down to afinal voltage of 2.8 V with a constant current of 0.2 C. After repeatingthis charge/discharge operation for 3 cycles, the battery was charged upto 4.35 V with a constant current of 0.2 C at a high temperature (60°C.) and then stored at a constant voltage of 4.35 V for 3 days. A gasgeneration amount after storing for 3 days was measured by theArchimedean method. As for the gas generation amount, a relative gasgeneration amount was examined on the basis of defining the gasgeneration amount of Comparative Example III-1 as 100%.

The results are shown in Tables 14 to 15.

TABLE 14 Proportion of compound Composition of SO₄ group-containingcompound (I) Other lithium salt (I) relative nonaqueous Content inContent in to total electrolytic nonaqueous nonaqueous mass of thesolution electrolytic electrolytic whole of Gas (Volume ratio ofsolution (% by solution electrolyte generation solvent) Kind mass) Kind(% by mass) salts (%) amount (%) Example III-1 EC/DEC/MEC (30/45/25)

 6 LiPF₆ 10 37.5 83 Example EC/MEC  6 10 37.5 85 III-2 (30/70) ExampleEC/VC/DEC/MEC  5 11 31.3 83 III-3 (29/1/40/30) Example EC/VC/DEC/MEC  610 37.5 81 III-4 (29/1/40/30) Example EC/VC/DEC/MEC  8  8 50   83 III-5(29/1/40/30) Example EC/VC/DEC/MEC 10  6 62.5 86 III-6 (29/1/40/30)Example EC/VC/DEC/MEC 16  0 100   88 III-7 (29/1/40/30)

TABLE 15 Proportion of SO₄ group-containing compound compound (I) Otherlithium salt (I) relative Content in Content in to total Composition ofnonaqueous nonaqueous mass of the nonaqueous electrolytic electrolyticelectrolytic whole of Gas solution solution (% solution electrolytegeneration (Volume ratio of solvent) Kind by mass) Kind (% by mass)salts (%) amount (%) Example III-8 EC/VC/DEC/MEC (29/1/40/30)

6 LiPF₆ (Class 1) 10   37.5 81 Example III-9 EC/VC/DEC/MEC (29/1/40/30)

6 37.5 82 Example III-10 EC/VC/DEC/MEC (29/1/40/30)

6 37.5 84 Example III-11 EC/FEC/VC/DEC/MEC (19/10/1/45/25)

6 LiPF₆ (Class 1) LiBF₆ (Class 1) 9.5   0.5 37.5 80 Example III-12EC/FEC/VC/DEC/MEC (19/10/1/45/25)

6 LiPF₆ (Class 1) LiN(SO₂F)₂ (Class 2) 9.5   0.5 37.5 78 Example III-13EC/FEC/VC/DEC/MEC (19/10/1/45/25)

6 LiPF₆ (Class 1) LiSO₃F (Class 3) 9.5   0.5 37.5 75 Example III-14EC/FEC/VC/DEC/MEC (19/10/1/45/25)

6 LiPF₆ (Class 1) LiPO₂F₂ (Class 4) 9.5   0.5 37.5 76 Example III-15EC/FEC/VC/DEC/MEC (19/10/1/45/25)

6 LiPF₆ (Class 1) LiPFO (Class 5) 9.5   0.5 37.5 77 ComparativeEC/VC/DEC/MEC None — LiPF₆ 16   0  100  Example (29/1/40/30) (Class 1)III-1 Comparative Example III-2 EC/VC/DEC/MEC (29/1/40/30)

6 LiPF₆ (Class 1) 10   37.5 102 

In all of the lithium secondary batteries of Examples III-1 to III-15,the effect for suppressing the gas generation after the high-temperaturestorage is remarkably improved as compared with the lithium secondarybatteries of Comparative Example III-1 in the case of not adding the SO₄group-containing compound represented by the general formula (I-3) andComparative Example III-2 in the case of adding lithium triflate as thelithium salt, in the nonaqueous electrolytic solution of the presentinvention. In the light of the above, it has been clarified that theeffect of the present invention is a peculiar effect to the case wherethe SO₄ group-containing compound specified in the present invention iscontained in the nonaqueous electrolytic solution having an electrolytesalt dissolved in a nonaqueous solvent.

Furthermore, the nonaqueous electrolytic solution of the presentinvention also has an effect for improving discharging properties of alithium primary battery in a broad temperature range.

<SO₄ Group-Containing Compound Represented by the General Formula (II)>Synthesis Example IV-1 Synthesis of Lithium2,2,3,3-Tetrafluorobutane-1,4-diyl Bis(sulfate) (Compound BA12)

To a slurry mixed liquid of 4.24 g (100 mmoles) of lithium chloride and100 g of dimethyl carbonate, 11.65 g (100 mmoles) of chlorosulfonic acidwas added dropwise at 10° C. or lower over 15 minutes. After stirring atroom temperature for 60 minutes, 8.10 g (50 mmoles) of2,2,3,3-tetrafluorobutane-1,4-diol was added dropwise over 15 minutes.After stirring this solution at room temperature for 3 hours, a crystalwas separated by filtration from a reaction solution being a slurry formand dried, thereby obtaining 13.36 g of lithium2,2,3,3-tetrafluorobutane-1,4-diylbis(sulfate) as a white crystal(yield: 80%).

The obtained lithium 2,2,3,3-tetrafluorobutane-1,4-diyl bis(sulfate) wassubjected to ¹H-NMR measurement to confirm its structure. The resultsare shown below.

¹H-NMR (400 MHz, DMSO-d6): δ (ppm)=4.16 (t, J=14.52 Hz, 4H)

Examples IV-1 to IV-12 and Comparative Examples IV-1 and IV-2 Productionof Lithium Ion Secondary Battery

94% by mass of LiCoO₂ and 3% by mass of acetylene black(electroconductive agent) were mixed and then added to and mixed with asolution which had been prepared by dissolving 3% by mass ofpolyvinylidene fluoride (binder) in 1-methyl-2-pyrrolidone in advance,thereby preparing a positive electrode mixture paste. This positiveelectrode mixture paste was applied onto one surface of an aluminum foil(collector), dried, and treated under pressure, followed by cutting intoa predetermined size, thereby producing a positive electrode sheet. Adensity of a portion of the positive electrode except for the collectorwas 3.6 g/cm³.

95% by mass of artificial graphite (d₀₀₂=0.335 nm, negative electrodeactive material) was added to and mixed with a solution which had beenprepared by dissolving 5% by mass of polyvinylidene fluoride (binder) in1-methyl-2-pyrrolidone in advance, thereby preparing a negativeelectrode mixture paste. This negative electrode mixture paste wasapplied onto one surface of a copper foil (collector), dried, andtreated under pressure, followed by cutting into a predetermined size,thereby producing a negative electrode sheet. A density of a portion ofthe negative electrode except for the collector was 1.5 g/cm³.

This electrode sheet was analyzed by means of X-ray diffraction, and asa result, a ratio [I(110)/I(004)] of a peak intensity I(110) of the(110) plane to a peak intensity I(004) of the (004) plane of thegraphite crystal was found to be 0.1.

The above-obtained positive electrode sheet, a micro-porous polyethylenefilm-made separator, and the above-obtained negative electrode sheetwere laminated in this order, and a nonaqueous electrolytic solutionhaving each of compositions shown in Table 16 was added thereto, therebyproducing 2032 coin-type batteries.

[Evaluation of Low-Temperature Properties after High-TemperatureCharging Storage]

<Initial Discharge Capacity>

In a thermostatic chamber at 25° C., each of the coin-type batteriesproduced by the aforementioned method was charged up to a final voltageof 4.2 V with a constant current of 1 C and under a constant voltage for3 hours; the temperature of the thermostatic chamber was then decreasedto −10° C.; and the battery was discharged down to a final voltage of2.75 V with a constant current of 1 C, thereby determining an initialdischarge capacity at −10° C.

<High-Temperature Charging Storage Test>

Subsequently, in a thermostatic chamber at 85° C., this coin-typebattery was charged up to a final voltage of 4.2 V with a constantcurrent of 1 C and under a constant voltage for 3 hours and then storedfor 3 days in a state of keeping at 4.2 V. Thereafter, the resultant wasput in a thermostatic chamber at 25° C. and then once discharged down toa final voltage of 2.75 V with a constant current of 1 C.

<Discharge Capacity after High-Temperature Charging Storage>

Furthermore, a discharge capacity at −10° C. after the high-temperaturecharging storage was then determined in the same manner as themeasurement of the initial discharge capacity.

<Low-Temperature Properties after High-Temperature Charging Storage>

The low-temperature properties after the high-temperature chargingstorage was determined from the following discharge capacity retentionrate at −10° C.

Discharge capacity retention rate (%) at −10° C. after high-temperaturecharging storage=(Discharge capacity at −10° C. after high-temperaturecharging storage)/(Initial discharge capacity at −10° C.)×100

The results are shown in Table 16.

TABLE 16 Composition of electrolyte salt Discharge Composition of SO₄group-containing compound (II) capacity nonaqueous Content in retentionrate at electrolytic nonaqueous −10° C. after solution electrolytichigh-temperature (Volume ratio of solution charging storage solvent)Kind (% by mass) at 85° C. (%) Example IV-1 1.1 M LiPF₆ EC/DEC (30/70)

0.3  68 Example IV-2 1.1 M LiPF₆ 0.01 70 EC/VC/DEC/MEC (29/1/40/30)Example IV-3 1.1 M LiPF₆ 0.3  76 EC/VC/DEC/MEC (29/1/40/30) Example IV-41.1 M LiPF₆ 3   74 EC/VC/DEC/MEC (29/1/40/30) Example IV-5 1.1 M LiPF₆EC/VC/DEC/MEC (29/1/40/30)

0.3  77 Example IV-6 1.1 M LiPF₆ EC/VC/DEC/MEC (29/1/40/30)

0.3  74 Example IV-7 1.1 M LiPF₆ EC/VC/DEC/MEC- (29/1/40/30)

0.3  72 Example IV-8 1.1 M LiPF₆ EC/VC/DEC/MEC (29/1/40/30)

0.3  71 Example IV-9 1.1 M LiPF₆ EC/VC/DEC/MEC (29/1/40/30)

0.3  78 Example IV-10 1.1 M LiPF₆ EC/VC/DEC/MEC (29/1/40/30)

0.3  69 Example IV-11 1.1 M LiPF₆ EC/VC/DEC/MEC (29/1/40/30)

0.3  71 Example IV-12 1.1 M LiPF₆ EC/VC/DEC/MEC (29/1/40/30)

0.3  72 Comparative 1.1 M LiPF₆ None — 65 Example IV-1 EC/VC/DEC/MEC(29/1/40/30) Comparative Example IV-2 1.1 M LiPF₆ EC/VC/DEC/MEC(29/1/40/30)

0.3  63

Example IV-13 and Comparative Example IV-3

A negative electrode sheet was produced by using silicon (elementalsubstance) (negative electrode active material) in place of the negativeelectrode active material used in Example IV-1. 80% by mass of silicon(elemental substance) and 15% by mass of acetylene black(electroconductive agent) were mixed and then added to and mixed with asolution which had been prepared by dissolving 5% by mass ofpolyvinylidene fluoride (binder) in 1-methyl-2-pyrrolidone in advance,thereby preparing a negative electrode mixture paste. Coin-typebatteries were produced in the same manner as in Example IV-1, exceptthat this negative electrode mixture paste was applied onto a copperfoil (collector), dried, and treated under pressure, followed by cuttinginto a predetermined size, thereby producing a negative electrode sheet,and that the composition of the nonaqueous electrolytic solution waschanged to a predetermined composition, and the batteries wereevaluated. The results are shown in Table 17.

TABLE 17 Composition of Discharge electrolyte salt SO₄ group-containingcompound (II) capacity Composition of Content in retention rate atnonaqueous nonaqueous −10° C. after electrolytic solution electrolytichigh-temperature (Volume ratio of solution charging storage solvent)Kind (% by mass) at 85° C. (%) Example IV-13 1.1 M LiPF₆ PC/FEC/DEC/MEC(15/15/40/30)

0.3 68 Comparative None — 49 Example IV-3

Example IV-14 and Comparative Example IV-4

90% by mass of LiMn_(1.5)Ni_(0.5)O₄ and 6% by mass of acetylene black(electroconductive agent) were mixed and then added to and mixed with asolution which had been prepared by dissolving 4% by mass ofpolyvinylidene fluoride (binder) in 1-methyl-2-pyrrolidone in advance,thereby preparing a positive electrode mixture paste. This positiveelectrode mixture paste was applied onto one surface of an aluminum foil(collector), dried, and treated under pressure, followed by cutting intoa predetermined size, thereby producing a positive electrode sheet. 80%by mass of Li₄Ti₅O₁₂ (negative electrode active material) and 15% bymass of acetylene black (electroconductive agent) were mixed and thenadded to and mixed with a solution which had been prepared by dissolving5% by mass of polyvinylidene fluoride (binder) in 1-methyl-2-pyrrolidonein advance, thereby preparing a negative electrode mixture paste. Thisnegative electrode mixture paste was applied onto one surface of acopper foil (collector), dried, and treated under pressure, followed bycutting into a predetermined size, thereby producing a negativeelectrode sheet. Then, the positive electrode sheet, a micro-porouspolyethylene film-made separator, and the negative electrode sheet werelaminated in this order, and a nonaqueous electrolytic solution havingthe composition shown in Table 18 was added thereto, thereby producing2032 coin-type batteries.

The batteries were evaluated in the same manner as in Example IV-1,except that in evaluating the battery, the final charging voltage andthe final discharging voltage were set to 3.5 V and 2.5 V, respectively;and that the composition of the nonaqueous electrolytic solution waschanged to a predetermined composition. The results are shown in Table18.

TABLE 18 Composition of Discharge electrolyte salt SO₄ group-containingcompound (II) capacity Composition of Content in retention rate atnonaqueous nonaqueous −10° C. after electrolytic solution electrolytichigh-temperature (Volume ratio of solution charging storage solvent)Kind (% by mass) at 85° C. (%) Example IV-14 1.2 M LiPF₆ EC/DEC/MEC(30/40/30)

0.3 59 Comparative None — 43 Example IV-4

Example IV-15

A lithium secondary battery was produced in the same manner as inComparative Example IV-1, except that a positive electrode produced byadding a predetermined amount of the SO₄ group-containing compoundrepresented by the general formula (II) relative to 100% of the positiveelectrode active material was used. The results are shown in Table 19.

Example IV-16

A lithium secondary battery was produced in the same manner as inExample IV-15, except that the SO₄ group-containing compound representedby the general formula (II) was not added to the positive electrode butadded to the negative electrode. The results are shown in Table 19.

TABLE 19 Composition of Discharge electrolyte salt capacity Compositionof SO₄ group-containing compound (II) retention rate at nonaqueousContent relative −10° C. after electrolytic solution to the activehigh-temperature (Volume ratio of material charging storage solvent)Kind Addition site (% by mass) at 85° C. (%) Example IV-15 1.1 M LiPF₆EC/VC/DEC/MEC (29/1/40/30)

Positive electrode 0.1 72 Example Negative 0.1 74 IV-16 electrode

In all of the lithium secondary batteries of Examples IV-1 to IV-12, theelectrochemical characteristics in a broad temperature range areremarkably improved as compared with the lithium secondary batteries ofComparative Example IV-1 in the case of not adding the SO₄group-containing compound represented by the general formula (II) andComparative Example IV-2 in the case of adding dimethyl sulfate, in thenonaqueous electrolytic solution of the present invention. In the lightof the above, it has been clarified that the effect of the presentinvention is a peculiar effect to the case where the lithium saltspecified in the present invention is contained in the nonaqueouselectrolytic solution having an electrolyte salt dissolved in anonaqueous solvent.

From comparison of Example IV-13 with Comparative Example IV-3 andcomparison of Example IV-14 with Comparative Example IV-4, the sameeffect is also seen even in the case of using silicon (elementalsubstance) Si or lithium titanate for the negative electrode, or thecase of using LiMn_(4.5)Ni_(0.5)O₄ for the positive electrode, andtherefore, it is evident that the effect of the present invention is notan effect relying on a specified positive electrode or negativeelectrode.

From comparison of Examples IV-15 and IV-16 with Comparative ExampleIV-1, even in the case of containing the SO₄ group-containing compoundrepresented by the general formula (II) in a site other than theelectrolytic solution, the effect is brought.

Furthermore, the nonaqueous electrolytic solution of the presentinvention also has an effect for improving discharging properties of alithium primary battery in a broad temperature range.

<SO₄ Group-Containing Compound Represented by the General Formula (III)or (IV)> Synthesis Example V-1 Synthesis of Ethyl Trimethylsilyl Sulfate(Compound CA10)

To a mixed liquid of 6.00 g (130 mmoles) of ethanol and 50 g ofdichloromethane, 16.69 g (143 mmoles) of chlorosulfonic acid was addeddropwise at 10° C. or lower over 15 minutes. After stirring at roomtemperature for 30 minutes, the resultant was again cooled, and 21.21 g(195 mmoles) of chlorotrimethylsilane was added dropwise at 10° C. orlower over 15 minutes. After refluxing this solution for 30 minutes, theresultant was distilled under reduced pressure, thereby obtaining 22.61g of ethyl trimethylsilyl sulfate from a main fraction distilled at76.5° C./3 torr (yield: 86%).

The obtained ethyl trimethylsilyl sulfate was subjected to ¹H-NMRmeasurement to confirm its structure. The results are shown below.

¹H-NMR (400 MHz, CDCl₃): δ (ppm)=4.32 (q, J=7.12 Hz, 2H), 1.41 (t,J=7.12 Hz, 3H), 0.43 (s, 9H)

Examples V-1 to V-25 and Comparative Examples V-1 and V-2 Production ofLithium Ion Secondary Battery

94% by mass of LiCoO₂ and 3% by mass of acetylene black(electroconductive agent) were mixed and then added to and mixed with asolution which had been prepared by dissolving 3% by mass ofpolyvinylidene fluoride (binder) in 1-methyl-2-pyrrolidone in advance,thereby preparing a positive electrode mixture paste. This positiveelectrode mixture paste was applied onto one surface of an aluminum foil(collector), dried, and treated under pressure, followed by cutting intoa predetermined size, thereby producing a positive electrode sheet. Adensity of a portion of the positive electrode except for the collectorwas 3.6 g/cm³.

95% by mass of artificial graphite (d₀₀₂=0.335 nm, negative electrodeactive material) was added to and mixed with a solution which had beenprepared by dissolving 5% by mass of polyvinylidene fluoride (binder) in1-methyl-2-pyrrolidone in advance, thereby preparing a negativeelectrode mixture paste. This negative electrode mixture paste wasapplied onto one surface of a copper foil (collector), dried, andtreated under pressure, followed by cutting into a predetermined size,thereby producing a negative electrode sheet. A density of a portion ofthe negative electrode except for the collector was 1.5 g/cm³.

This electrode sheet was analyzed by means of X-ray diffraction, and asa result, a ratio [I(110)/I(004)] of a peak intensity I(110) of the(110) plane to a peak intensity I(004) of the (004) plane of thegraphite crystal was found to be 0.1.

The above-obtained positive electrode sheet, a micro-porous polyethylenefilm-made separator, and the above-obtained negative electrode sheetwere laminated in this order, and a nonaqueous electrolytic solutionhaving each of compositions shown in Tables 20 to 22 was added thereto,thereby producing 2032 coin-type batteries.

[Evaluation of Low-Temperature Properties after High-TemperatureCharging Storage]

<Initial Discharge Capacity>

In a thermostatic chamber at 25° C., each of the coin-type batteriesproduced by the aforementioned method was charged up to a final voltageof 4.2 V with a constant current of 1 C and under a constant voltage for3 hours; the temperature of the thermostatic chamber was then decreasedto −10° C.; and the battery was discharged down to a final voltage of2.75 V with a constant current of 1 C, thereby determining an initialdischarge capacity at −10° C.

<High-Temperature Charging Storage Test>

Subsequently, in a thermostatic chamber at 65° C., this coin-typebattery was charged up to a final voltage of 4.2 V with a constantcurrent of 1 C and under a constant voltage for 3 hours and then storedfor 5 days in a state of keeping at 4.2 V. Thereafter, the resultant wasput in a thermostatic chamber at 25° C. and then once discharged down toa final voltage of 2.75 V with a constant current of 1 C.

<Discharge Capacity after High-Temperature Charging Storage>

Furthermore, a discharge capacity at −10° C. after the high-temperaturecharging storage was then determined in the same manner as themeasurement of the initial discharge capacity.

<Low-Temperature Properties after High-Temperature Charging Storage>

The low-temperature properties after the high-temperature chargingstorage were determined from the following discharge capacity retentionrate at −10° C.

Discharge capacity retention rate (%) at −10° C. after high-temperaturecharging storage=(Discharge capacity at −10° C. after high-temperaturecharging storage)/(Initial discharge capacity at −10° C.)×100

<High-Temperature Cycle Properties>

In a thermostatic chamber at 65° C., each of the batteries produced bythe aforementioned method was treated by repeating a cycle of chargingup to a final voltage of 4.2 V with a constant current of 1 C and undera constant voltage for 3 hours and subsequently discharging down to adischarge voltage of 3.0 V with a constant current of 1 C, until itreached 200 cycles. Then, a discharge capacity retention rate after thecycles was determined according to the following equation.

Discharge capacity retention rate (%)=(Discharge capacity after 200cycles)/(Discharge capacity after 1st cycle)×100

The results are shown in Tables 20 to 22.

TABLE 20 Discharge Composition of SO₄ group-containing compound (III)capacity electrolyte salt Content in retention rate at Composition ofnonaqueous −10° C. after nonaqueous electrolytic electrolytichigh-temperature solution solution charging storage (Volume ratio ofsolvent) Kind (% by mass) at 65° C. (%) Example V-1 1.15 M LiPF₆EC/DMC/MEC (30/45/25)

1   74 Example 1.15 M LiPF₆ 1   70 V-2 EC/MEC (30/70) Example 1.15 MLiPF₆ 0.08 76 V-3 EC/VC/DMC/MEC (29/1/40/30) Example 1.15 M LiPF₆ 1   80V-4 EC/VC/DMC/MEC (29/1/40/30) Example 1.15 M LiPF₆ 3   78 V-5EC/VC/DMC/MEC (29/1/40/30)

TABLE 21 Composition of SO₄ group-containing compound Dischargeelectrolyte salt (III) or (IV) capacity Composition of Content inretention rate at nonaqueous electrolytic nonaqueous −10° C. aftersolution electrolytic high-temperature (Volume ratio of solutioncharging storage solvent) Kind (% by mass) at 65° C. (%) Example V-6 1.1M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

1 80 Example V-7 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

1 78 Example V-8 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

1 77 Example V-9 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

1 79 Example V-10 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

1 78 Example V-11 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

1 79 Example V-12 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

1 79 Example V-13 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

1 77 Example V-14 1.1 M LiPF₆ + 0.05 M LiPO₂F₂ EC/VC/DMC/MEC(29/1/45/25)

1 85 Example V-15 0.7 M LiPF₆ + 0.45 M LiTFSI EC/VC/DMC/MEC (29/1/45/25)

1 86 Example V-16 1.1 M LiPF₆ + 0.05 M LiBOB EC/FEC/VC/DMC/MEC(19/10/1/45/25)

1 84

TABLE 22 Composition of electrolyte salt SO₄ group-containing compoundDischarge Composition of (III) or (IV) capacity nonaqueous Content inretention rate at electrolytic nonaqueous −10° C. after solutionelectrolytic high-temperature (Volume ratio of solution charging storagesolvent) Kind (% by mass) at 65° C. (%) Example V-17 1.1 M LiPF₆EC/VC/DMC/MEC (29/1/45/25)

1   77 Example V-18 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

1   78 Example V-19 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

1   81 Example V-20 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

1   81 Example V-21 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

1   73 Example V-22 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

1   72 Example V-23 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25) + Lithiummethyl sulfate (0.18 wt %)

0.12 77 Example V-24 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

0.3  76 Example V-25 1.1 M LiPF₆ EC/VC/DMC/MEC (29/1/45/25)

1   81 Comparative 1.1 M LiPF₆ None — 60 Example V-1 EC/VC/DMC/MEC(29/1/45/25) Comparative Example V-2 1.1 M LiPF₆ EC/VC/DMC/MEC(29/1/45/25)

1   59

Example V-26 and Comparative Example V-3

A negative electrode sheet was produced by using silicon (elementalsubstance) (negative electrode active material) in place of the negativeelectrode active material used in Example V-1. 80% by mass of silicon(elemental substance) and 15% by mass of acetylene black(electroconductive agent) were mixed and then added to and mixed with asolution which had been prepared by dissolving 5% by mass ofpolyvinylidene fluoride (binder) in 1-methyl-2-pyrrolidone in advance,thereby preparing a negative electrode mixture paste. Coin-typebatteries were produced in the same manner as in Example V-1, exceptthat this negative electrode mixture paste was applied onto a copperfoil (collector), dried, and treated under pressure, followed by cuttinginto a predetermined size, thereby producing a negative electrode sheet,and that the composition of the nonaqueous electrolytic solution waschanged to a predetermined composition, and the batteries wereevaluated. The results are shown in Table 23.

TABLE 23 Composition of Discharge electrolyte salt SO₄ group-containingcompound (III) capacity Composition of Content in retention rate atnonaqueous electrolytic nonaqueous −10° C. after solution electrolytichigh-temperature (Volume ratio of solution charging storage solvent)Kind (% by mass) at 65° C. (%) Example V-26 1.2 M LiPF₆ PC/FEC/DMC/MEC(15/15/45/25)

1 71 Comparative None — 46 Example V-3

Example V-27 and Comparative Example V-4

90% by mass of LiMn_(1.5)Ni_(0.5)O₄ and 6% by mass of acetylene black(electroconductive agent) were mixed and then added to and mixed with asolution which had been prepared by dissolving 4% by mass ofpolyvinylidene fluoride (binder) in 1-methyl-2-pyrrolidone in advance,thereby preparing a positive electrode mixture paste. This positiveelectrode mixture paste was applied onto one surface of an aluminum foil(collector), dried, and treated under pressure, followed by cutting intoa predetermined size, thereby producing a positive electrode sheet.

80% by mass of Li₄Ti₅O₁₂ (negative electrode active material) and 15% bymass of acetylene black (electroconductive agent) were mixed and thenadded to and mixed with a solution which had been prepared by dissolving5% by mass of polyvinylidene fluoride (binder) in 1-methyl-2-pyrrolidonein advance, thereby preparing a negative electrode mixture paste. Thisnegative electrode mixture paste was applied onto one surface of acopper foil (collector), dried, and treated under pressure, followed bycutting into a predetermined size, thereby producing a negativeelectrode sheet.

The above-obtained positive electrode sheet, a micro-porous polyethylenefilm-made separator, and the above-obtained negative electrode sheetwere laminated in this order, and a nonaqueous electrolytic solutionhaving the composition shown in Table 24 was added thereto, therebyproducing 2032 coin-type batteries.

The batteries were evaluated in the same manner as in Example V-1,except that in evaluating the battery, the final charging voltage andthe final discharging voltage were set to 3.5 V and 2.5 V, respectively;and that the composition of the nonaqueous electrolytic solution waschanged to a predetermined composition. The results are shown in Table24.

TABLE 24 Composition of Discharge electrolyte salt SO₄ group-containingcompound (III) capacity Composition of Content in retention rate atnonaqueous nonaqueous −10° C. after electrolytic solution electrolytichigh-temperature (Volume ratio of solution charging storage solvent)Kind (% by mass) at 65° C. (%) Example V-27 1.2 M LiPF₆ PC/DEC (30/70)

1 60 Comparative None — 45 Example V-4

Example V-28

A lithium secondary battery was produced in the same manner as inComparative Example V-1, except that a positive electrode produced byadding a predetermined amount of the compound of the present inventionrelative to 100% of the positive electrode active material was used. Theresults are shown in Table 25.

Example V-29

A lithium secondary battery was produced in the same manner as inExample V-28, except that the compound of the present invention was notadded to the positive electrode but added to the negative electrode. Theresults are shown in Table 25.

TABLE 25 Composition of Discharge electrolyte salt capacity Compositionof retention rate at nonaqueous SO₄ group-containing compound (IV) −10°C. after electrolytic solution Content relative to high-temperature(Volume ratio of the active material charging storage solvent) KindAddition site (% by mass) at 65° C. (%) Example V-28 1.1 M LiPF₆EC/VC/DMC/MEC (29/1/45/25)

Positive electrode 0.3 74 Example Negative 0.3 73 V-29 electrode

In all of the lithium secondary batteries of Examples V-1 to V-25, theelectrochemical characteristics in a broad temperature range areremarkably improved as compared with the lithium secondary batteries ofComparative Example V-1 in the case of not adding the SO₄group-containing compound represented by the general formula (III) or(IV) and Comparative Example V-2 in the case of adding dimethyl sulfate,in the nonaqueous electrolytic solution of the present invention. In thelight of the above, it has been clarified that the effect of the presentinvention is a peculiar effect to the case where the SO₄group-containing compound according to the present invention iscontained in the nonaqueous electrolytic solution having an electrolytesalt dissolved in a nonaqueous solvent. In addition, the dischargecapacity retention rates of the lithium secondary battery produced underthe same conditions as those in Example V-4 and Comparative Examples V-1and V-2 after 200 cycles at 65° C. are 72%, 66%, and 67%, respectively.Thus, in the battery using the nonaqueous electrolytic solution havingthe SO₄ group-containing compound according to the present inventionadded thereto, the discharge capacity retention rate after 200 cycles at65° C. was also remarkably improved relative to Comparative Examples V-1and V-2.

From comparison of Example V-26 with Comparative Example V-3 andcomparison of Example V-27 with Comparative Example V-4, the same effectis also seen even in the case of using silicon (elemental substance) Sior lithium titanate for the negative electrode, it is evident that theeffect of the present invention is not an effect relying on a specifiedpositive electrode or negative electrode.

From comparison of Examples V-28 and V-29 with Comparative Example V-1,even in the case of containing the SO₄ group-containing compoundaccording to the present invention in a site other than the electrolyticsolution, the effect is brought.

Furthermore, the nonaqueous electrolytic solution of the presentinvention also has an effect for improving discharging properties of alithium primary battery in a broad temperature range.

INDUSTRIAL APPLICABILITY

By using the nonaqueous electrolytic solution of the present invention,an energy storage device having excellent electrochemicalcharacteristics in a broad temperature range can be obtained. Inparticular, when the nonaqueous electrolytic solution of the presentinvention is used as a nonaqueous electrolytic solution for an energystorage device, such as a lithium secondary battery mounted in a hybridelectric vehicle, a plug-in hybrid electric vehicle, a battery electricvehicle, etc., an energy storage device whose electrochemicalcharacteristics are hardly worsened in a broad temperature range can beobtained.

1. A nonaqueous electrolytic solution, comprising: an electrolyte saltdissolved in a nonaqueous solvent; and as an additive, at least one SO₄group-containing compound selected from the group consisting ofcompounds represented by the following formulae (I) to (IV):

wherein: L¹ represents an alkyl group having 1 to 12 carbon atoms, analkoxyalkyl group having 2 to 12 carbon atoms, an aryl group having 6 to12 carbon atoms, an alkenyl group having 2 to 7 carbon atoms, an alkynylgroup having 3 to 8 carbon atoms, a linear or cyclic ester group having3 to 18 carbon atoms, a sulfur atom-containing organic group having 1 to6 carbon atoms, a silicon atom-containing organic group having 4 to 10carbon atoms, a cyano group-containing organic group having 2 to 7carbon atoms, a phosphorus atom-containing organic group having 2 to 12carbon atoms, a —P(═O)F₂ group, an alkylcarbonyl group having 2 to 7carbon atoms, or an arylcarbonyl group having 7 to 13 carbon atoms,provided that each of the alkyl group, the alkoxyalkyl group, thealkenyl group, the alkynyl group, and the alkylcarbonyl group isstraight-chain or branched, and in each of the alkyl group, thealkoxyalkyl group, the aryl group, the ester group, the sulfuratom-containing organic group, the phosphorus atom-containing organicgroup, the alkylcarbonyl group, and the arylcarbonyl group, at least onehydrogen atom may be substituted with a halogen atom; L² represents ap-valent hydrocarbon connecting group optionally comprising an etherbond, a thioether bond, or an —S(═O)₂ bond, provided that at least onehydrogen atom which L² has may be substituted with a halogen atom; ρ isan integer of 2 to 4; each of R³¹ to R³³ independently represents analkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 3carbon atoms, or an aryl group having 6 to 8 carbon atoms; q is aninteger of 1 to 4; when q is 1, then R³¹ may be —OSO₃—R³⁷, and R³⁷ issynonymous with R³¹; when q is 1, then L³ represents an alkyl grouphaving 1 to 12 carbon atoms, an alkenyl group having 2 to 6 carbonatoms, an alkynyl group having 3 to 6 carbon atoms, an alkoxyalkyl grouphaving 2 to 12 carbon atoms, a —CR³⁴R³⁵C(═O)OR³⁶ group, or an aryl grouphaving 6 to 12 carbon atoms; when q is 2 to 4, then L³ represents aq-valent hydrocarbon connecting group which may contain an ether bond, athioether bond, or an —S(═O)₂— bond; each of R³⁴ and R³⁵ independentlyrepresents a hydrogen atom, a halogen atom, or an alkyl group having 1to 4 carbon atoms, and R³⁶ represents an alkyl group having 1 to 8carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or an alkynylgroup having 3 to 6 carbon atoms; in each of the alkyl group and thearyl group represented by L³ and the alkyl group represented by each ofR³⁴ to R³⁶, at least one hydrogen atom may be substituted with a halogenatom; L⁴ represents an alkyl group having 1 to 12 carbon atoms, analkenyl group having 2 to 6 carbon atoms, an alkynyl group having 3 to 6carbon atoms, an alkoxyalkyl group having 2 to 12 carbon atoms, a—CR⁴¹C⁴²C(═O)OR⁴³ group, or an aryl group having 6 to 12 carbon atoms, Xrepresents an SiR⁴⁴R⁴⁵ group, a quaternary onium, an alkali metalbelonging to the third or fourth period of the Periodic Table, or analkaline earth metal belonging to the third or fourth period of thePeriodic Table; r is an integer of 1 or 2, provided that when X is aquaternary onium or an alkali metal belonging to the third or fourthperiod of the Periodic Table, then r is 1, and when X is an SiR⁴⁴R⁴⁵group or an alkaline earth metal belonging to the third or fourth periodof the Periodic Table, then r is 2; each of R⁴¹ and R⁴² independentlyrepresents a hydrogen atom, a halogen atom, or an alkyl group having 1to 4 carbon atoms; R⁴³ represents an alkyl group having 1 to 8 carbonatoms, an alkenyl group having 2 to 6 carbon atoms, or an alkynyl grouphaving 3 to 6 carbon atoms; each of R⁴⁴ and R⁴⁵ independently representsan alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to3 carbon atoms, or an aryl group having 6 to 8 carbon atoms; and in eachof the alkyl group and the aryl group represented by L⁴ and the alkylgroup represented by each of R⁴¹ to R⁴³, at least one hydrogen atom maybe substituted with a halogen atom.
 2. The nonaqueous electrolyticsolution according to claim 1, wherein a content of the SO₄group-containing compound in the nonaqueous electrolytic solution is0.001 to 5% by mass in total.
 3. The nonaqueous electrolytic solutionaccording to claim 1, comprising the SO₄ group-containing compoundrepresented by the general formula (I), which is a compound representedby formula (I-1), (I-2), or (I-3):

wherein: L¹¹ represents an alkyl group having 1 to 12 carbon atoms, analkoxyalkyl group having 2 to 12 carbon atoms, or an aryl group having 6to 12 carbon atoms, provided that in each of the alkyl group, thealkoxyalkyl group, and the aryl group, at least one hydrogen atom may besubstituted with a halogen atom; L¹² represents a straight-chain orbranched alkenyl group having 2 to 7 carbon atoms, a straight-chain orbranched alkynyl group having 3 to 8 carbon atoms, a linear or cyclicester group having 3 to 18 carbon atoms, a linear or cyclic carbonategroup having 3 to 18 carbon atoms, a sulfur atom-containing organicgroup having 1 to 6 carbon atoms, a silicon atom-containing organicgroup having 4 to 10 carbon atoms, a cyano group-containing organicgroup having 2 to 7 carbon atoms, a phosphorus atom-containing organicgroup having 2 to 12 carbon atoms, a —P(═O)F₂ group, an alkylcarbonylgroup having 2 to 7 carbon atoms, or an arylcarbonyl group having 7 to13 carbon atoms, provided that each of the alkenyl group, the alkynylgroup, and the alkylcarbonyl group is straight-chain or branched, and ineach of the ester group, the sulfur atom-containing organic group, thephosphorus atom-containing organic group, the alkylcarbonyl group, andthe arylcarbonyl group, at least one hydrogen atom may be substitutedwith a halogen atom; and L¹³ represents an alkyl group having 1 to 12carbon atoms, in which at least one hydrogen atom is substituted with ahalogen atom, an alkoxyalkyl group having 2 to 12 carbon atoms, in whichat least one hydrogen atom is substituted with a halogen atom, or anaryl group having 6 to 12 carbon atoms, in which at least one hydrogenatom is substituted with a halogen atom.
 4. The nonaqueous electrolyticsolution according to claim 3, comprising the SO₄ group-containingcompound represented by formula (I-1), which is at least one selectedfrom the group consisting of lithium methyl sulfate, lithium ethylsulfate, lithium propyl sulfate, lithium butyl sulfate, lithium pentylsulfate, lithium hexyl sulfate, lithium heptyl sulfate, lithium octylsulfate, lithium isopropyl sulfate, lithium sec-butyl sulfate, lithiumtrifluoromethyl sulfate, lithium 2,2,2-trifluoroethyl sulfate, lithium2,2,3,3-tetrafluoropropyl sulfate, lithium1,1,1,3,3,3-hexafluoro-2-propyl sulfate, lithium methoxyethyl sulfate,lithium ethoxyethyl sulfate, lithium methoxypropyl sulfate, lithiumphenyl sulfate, lithium 4-methylphenyl sulfate, lithium 4-fluorophenylsulfate, and lithium perfluorophenyl sulfate.
 5. The nonaqueouselectrolytic solution according to claim 3, comprising the SO₄group-containing compound represented by formula (I-2), which is atleast one selected from the group consisting of lithium vinyl sulfate,lithium allyl sulfate, lithium propargyl sulfate, lithium1-oxo-1-ethoxy-1-oxopropan-2-yl sulfate, lithium1-oxo-1-(2-propynyloxy)propan-2-yl sulfate, lithium 2-(acryloyloxy)ethylsulfate, lithium 2-(methacryloyloxy)ethyl sulfate, lithium2-((methoxycarbonyl)oxy)ethyl sulfate, lithium(2-oxo-1,3-dioxolan-4-yl)methyl sulfate, lithium2-(methanesulfonyl)ethyl sulfate, lithium methanesulfonyl sulfate,lithium trifluoromethanesulfonyl sulfate, lithium2-(trimethylsilyl)ethyl sulfate, lithium 2-cyanoethyl sulfate, lithium1,3-dicyanopropynyl 2-sulfate, lithium (diethoxyphosphoryl)methylsulfate, lithium diethoxyphosphoryl sulfate, lithium dibutoxyphosphorylsulfate, and lithium difluorophosphoryl sulfate.
 6. The nonaqueouselectrolytic solution according to claim 3, comprising the SO₄group-containing compound represented by formula (I-3), wherein aconcentration of the SO₄ group-containing compound in the nonaqueouselectrolytic solution is 5% by mass or more.
 7. The nonaqueouselectrolytic solution according to claim 6, wherein the compoundrepresented by the general formula (I-3) is present in a proportion of25% or more relative to a total mass of electrolyte salts in thenonaqueous electrolytic solution.
 8. The nonaqueous electrolyticsolution according to claim 1, wherein the nonaqueous solvent comprisesa cyclic carbonate and a linear carbonate.
 9. The nonaqueouselectrolytic solution according to claim 8, wherein the cyclic carbonatecomprises at least one selected from the group consisting of ethylenecarbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylenecarbonate, and a cyclic carbonate having a carbon-carbon unsaturatedbond or a fluorine atom.
 10. The nonaqueous electrolytic solutionaccording to claim 9, wherein the cyclic carbonate comprises a cycliccarbonate having a carbon-carbon unsaturated bond which is at least oneselected from the group consisting of vinylene carbonate, vinyl ethylenecarbonate, and 4-ethynyl-1,3-dioxolan-2-one.
 11. The nonaqueouselectrolytic solution according to claim 9, wherein the cyclic carbonatecomprises a cyclic carbonate having a fluorine atom which is at oneselected from the group consisting of 4-fluoro-1,3-dioxolan-2-one andtrans-4,5-difluoro-1,3-dioxolan-2-one andcis-4,5-difluoro-1,3-dioxolan-2-one.
 12. The nonaqueous electrolyticsolution according to claim 8, wherein the nonaqueous solvent comprisesa linear carbonate which is a symmetric linear carbonate or anasymmetric linear carbonate.
 13. The nonaqueous electrolytic solutionaccording to claim 12, wherein the nonaqueous solvent comprises anasymmetric linear carbonate which is at least one selected from thegroup consisting of methyl ethyl carbonate, methyl propyl carbonate,methyl isopropyl carbonate, methyl butyl carbonate, and ethyl propylcarbonate.
 14. The nonaqueous electrolytic solution according to claim12, wherein the nonaqueous solvent comprises a symmetric linearcarbonate which is at least one selected from the group consisting ofdimethyl carbonate, diethyl carbonate, dipropyl carbonate, and dibutylcarbonate.
 15. The nonaqueous electrolytic solution according to claim1, further comprising a fluorine-containing compound represented byformula (V):

wherein each of R⁵¹ to R⁵³ independently represents an alkyl grouphaving 1 to 12 carbon atoms, an alkenyl group having 2 to 3 carbonatoms, an aryl group having 6 to 8 carbon atoms, or an S(═O)₂F group.16. The nonaqueous electrolytic solution according to claim 1, whereinthe electrolyte salt comprises at least one lithium salts selected fromthe group consisting of LiPF₆, LiBF₄, LiSO₃F, lithiumtrifluoro((methanesulfonyl)oxy)borate, LiPO₂F₂, LiN(SO₂CF₃)₂,LiN(SO₂F)₂, lithium bis[oxalate-O,O′]borate, and lithiumdifluorobis[oxalate-O,O′]phosphate.
 17. An energy storage device,comprising: a positive electrode; a negative electrodes; and thenonaqueous electrolytic solution of claim
 1. 18. An energy storagedevice, comprising: a positive electrode; a negative electrode; and thenonaqueous electrolytic solution of claim
 6. 19. The energy storagedevice according to claim 17, wherein an active material of the positiveelectrode is a complex metal oxide comprising lithium and at least oneselected from the group consisting of cobalt, manganese, and nickel, ora lithium-containing olivine-type phosphate comprising at least oneselected from the group consisting of iron, cobalt, nickel, andmanganese.
 20. The energy storage device according to claim 17, whereinan active material of the negative electrode comprises at least oneselected from the group consisting of a lithium metal, a lithium alloy,a carbon material capable of absorbing and releasing lithium, tin, a tincompound, silicon, a silicon compound, and a lithium titanate compound.